Solve by using the elimination method.

9x-y=72
x+4y=45

9x-y=72

x+4y=45
get either x to be same value or y... in this case i chose y
4(9x-y=72)
x+4y=45
so
36x-4y=288
x+4y=45
so
37x=333
x= 9
then plug 9 into one of the equation to get y.