I don't really understand you questions, is it find y?
x + 2y =3
-x +3y = 2 (you can switch the x and y positions)
5y = 5 (I added knowing x is different sign same coefficient they cancel)
y = 1 (divided 5 on both sides)
Find x by substituting in either equation.
x + 2*1 = 3 (substituting y =1 in the first equation)
x = 1 (subtracted 2 on both sides)