I like using elimination method. So to do this you add the two exquations together. You get 3x+2y=73.. Wait that wont work. So now you have to change an question that is fair with math, what i would do, is multiply both sides of the x+y=28 by -1, to get -x+ -y=-28, now add them together. x=15, cool right? Now Solve for y. Take x+y=28, plug in x, 15+y=28; subtract 15 from each side, y=28-15; simplify, y=13. Hope i helped :)
