Since previous poster was not familier with
Economics, and you did not explain the
context, he thought you wanted to plot
Income as a function of X and Y. Of course,
what you want is Y as a function of X with
Income, P1, and P2 given numerical values,
in other words a budget constraint.
Essentially what you have is a very simple
implicit function.

You can do this with the following simple
code where you replace the ?'s with
numbers:

Income:= ?; P1:=?; P2:= ?;
plot((Income-P1*X)/P2,X=0..Income/P1);