As long as you can rely that your source string is always 4 characters after removal of the column below should work.
If you can't be sure then please provide representative "have" sample data with all the potential patterns the code needs to work for.
data have;
input MotherHeight $;
MHInch=sum(
input(substr(MotherHeight,1,2),best32.)*12
,input(substr(compress(MotherHeight,':'),3,2),best32.)
);
datalines;
05:03
0503
;
Code like below could help you figure out what patterns you're dealing with.
proc sql;
select distinct
prxchange('s/\d/9/',-1,strip(MotherHeight)) as pattern
from have
;
quit;