Find three solution of equation 4x+3y=12

Pls! does anybody know a shortcut for answering these types of questions in the future?

Which equation results from adding the equations in this system? x+6y=9 and -x+2y=-15

Money off coupons have been circulated to 300 households. only 2/5 of these were redeemed (used) in the local supermarket to get a free shampoo. what fraction of coupons were unused? (ps: write how you got the answer)