The Link you have provided it almost tells every thing.In your case the Rsqure is is only .40 that means there are other variables which are accounted for .60 or 60%. Your Adj Rsquare is even more less 37% . Find out all those variables and do multiple regression . Your plots (No1)looks dont look like a fan shape or semicircle that which menas it is ok . You have one outlier as per the C'D panel (No 6).
Sayng so , please have a look at your data , Remove the outlier.Please understand with the theory first. I am also just learning ,but not reached Regression Analysis yet .so i could not provide much ,may be others can help.
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