Stuck on implenting a new variable into my program

[Godzilla_Hat]

data cars;
input  make $ vol hp mpg sp wt;
datalines; 
Audi200QuatroWag     132     162     23.1     121     40
BMW750IL             119     295     16.7     157     45
BuickElectraWagon    160     140     22.9     110     45
BuickReatta           50     165     23.6     122     40
CadillacBrougham     129     140     22.9     110     45
CadillacBrougham     129     175     19.5     121     45
ChevroletBeretta     106      95     32.2     106     30
ChevroletCaprice     131     140     25.3     114     40
ChevroletCorsica     113      95     32.2     106     30
ChryslerLebaronConv   94     100     28.0     104     35
ChryslerNewYorker    121     150     23.6     117     40
DaihatsuCharade       92      53     46.5      96     20
DaihatsuCharade       94      80     43.4     107     22.5
DodgeColt             96      81     39.3     105     25
DodgeDaytona          99     100     31.5     108     30
DodgeDynasty         115     100     28.0     105     35
DodgeShadow          102      93     31.5     105     30
EagleSpirit          111     100     31.4     108     30
EagleSummit          101      81     35.1     102     27.5
FordEscort           103      90     42.2     109     25
FordEscort           101      84     36.1     103     27.5
FordEscortWagon      114      84     36.1     103     27.5
FordMustang           92      96     28.0     102     35
FordTempo            103      98     31.4     107     30
FordThunderbird      116     120     25.6     107     40
GM/GeoMetro           92      55     56.0      97     20
GM/GeoMetroLSI        92      55     55.9      97     20
GM/GeoMetroXF1        89      49     65.4      96     17.5
GM/GeoPrism           97     102     35.4     111     27.5
GM/GeoSprint          92      55     45.4      97     20
GM/GeoSprintTurbo     89      70     46.2     105     20
GM/GeoStorm           89      95     38.8     111     25
HondaCivic            99      92     40.9     113     22.5
HondaCivic            99      92     40.9     110     25
HondaCivic            99      92     38.4     110     25
HondaCivicCRX         50      92     40.9     113     22.5
HondaCivicCRX         50      92     38.8     113     22.5
HondaCivicCRX         50      92     38.4     110     25
HondaCivicCRXHF       50      62     59.2      98     22.5
HondaCivicCRXHF       50      62     53.3      98     22.5
HondaCivicWagon      117      92     38.4     110     25
IsuzuStylus          101      95     40.0     111     25
JaguarXJSConvert      50     263     17.0     147     45
LexusLS400           112     245     23.5     148     40
LincolnContinental   123     140     23.9     114     40
Mazda323Protege      107     103     36.3     112     27.5
Mercedes500SL         50     322     18.1     165     45
Mercedes560SEL       115     238     17.2     140     45
Nissan300ZX           50     280     23.4     160     40
NissanCentraCoupe     98      90     35.1     106     27.5
NissanCentraWagon     88      90     35.0     106     27.5
OldsCutlassSup       113     180     30.4     133     35
OldsCutlassSup       113     160     28.9     125     35
Oldsmobile98         127     165     23.6     122     40
OldsTrof/Toronado    114     165     23.6     122     40
PontiacBonneville    123     165     23.6     122     40
PontiacLeMans        107      74     40.7     101     25
PontiacSunbirdConv    88      95     32.2     106     30
Rolls-RoyceVarious   107     236     13.2     130     55
Saab9000             124     130     28.0     115     35
SubaruLoyale         102      90     29.5     109     25
SubaruJusty           89      73     41.1     103     22.5
SubaruJusty           89      73     40.4     103     22.5
SubaruJusty           89      66     39.6     100     22.5
SubaruJusty4wd        89      73     39.3     103     22.5
SuzukiSwift           92      70     49.0     105     20
ToyotaCamry          101     115     33.7     109     35
ToyotaCamry          101     115     32.6     109     35
ToyotaCamry          101     115     31.3     109     35
ToyotaCamry          101     115     28.0     109     35
ToyotaCamryWagon     124     115     31.3     109     35
ToyotaCelica          86     102     33.2     109     30
ToyotaCelica          86     102     32.9     109     30
ToyotaCelica          86     130     31.2     120     30
ToyotaCorolla        113     102     35.3     111     27.5
ToyotaCorolla         92     130     32.3     120     30
ToyotaCorolla         92     102     32.2     109     30
ToyotaTercel          91      78     38.9     106     22.5
ToyotaTercel          91      78     38.2     106     22.5
VolksJettaDiesel     104      52     46.9      90     27.5
Volvo740             111     145     27.7     120     35
Volvo760Wagon        135     162     23.4     121     40
;


PROC PRINT DATA=cars;
RUN;

a.Create a new variable called Density which is determined by the vehicle weight (WT x 100) divided by the vehicle’s volume (VOL).

Print the 21st through the 30th observations from the data set including the new variable value.

b. b.Create a categorical variable, FuelEcon, based on the values of MPG in the data set.

Let Category 1 include all vehicles below 20.0 MPG, 2 = 20.0 to 29.9 MPG, 3 = 30.0 to 39.9, 4 = 40.0 to 49.9, and 5 includes anything 50 MPG or above.

Print just the Model and the FuelEconvariables for the entire data set.

I'm stuck on creating these variables for this data set. How would I go about doing this ? ( Part a and b should be seperate from each other) 

[SASKiwi]

To get you started, add this statement to your program for question a. Note doing maths in SAS is very similar to writing it by hand but using characters on the keyboard to substitute the mathematical ones. 

Density = (wt * 100) / vol;

[tarheel13]

You need to use if else statements to create the categorical variable. Otherwise, you could use proc format to create a new format and create a new variable with a put statement and apply the format to mpg variable. I prefer to just use the if-else statements. 

data cars2;
	set cars;
	density = (wt* 100)/ vol;
run;

title "Density variable for obs 21 - 30";
proc print data=cars2 (firstobs=21 obs=30);
	var wt vol density;
run;
title;

data categories;
	set cars;
	
	*create FuelEcon;
	if ^missing(MPG) and mpg < 20.0 then fuelecon=1;
	else if 20.0 <= mpg < 30.0 then fuelecon=2;
	else if 30.0 <= mpg < 40.0 then fuelecon=3;
	else if 40.0 <= mpg < 50.0 then fuelecon=4;
	else if mpg >= 50 then fuelecon=5;
	
run;

title "Check derivation of fuelecon variable";
proc means data=categories n nmiss min max;
	class fuelecon / missing;
	var mpg;
run;

title;

title "Print model and fuelecon for categories ds";
proc print data=categories;
	var make fuelecon;
run;
title;