There are basically three proper methods to do so.
1.Elimination Method(the best): 3x +2y =5 ; 3x + 5y =8
So, ( 3x + 5y)- (3x +2y)=8-5. where 3x will get eliminated
5y -2y=3; 3y=3 ; y=1. PRETTY EASY!
If you do not get the same terms ( 3x in this case) just multiply the equations on both sides by the LCM of the term to be eliminated.