Solve for both systems: 5x + 3y = 72 and - x + 3y = 18

- x + 3y = 18

- x+x+ 3y = 18+x

3y = 18+x

3y-18 = 18-18+x

3y-18 =x

5x + 3y = 72

5(3y-18) + 3y = 72

5(3y) (5)(-18) + 3y = 72

15y-90+3y=72

18y-90=72

18y-90+90=72+90

18y=162

18y/18=162/18

y=9

3y-18 =x

3(9)-18 =x

27-18 =x

9=x