8x + 7y = -15 (1st)
-7x - 9y = -7 (2nd)
multiply (1st) by 7 and (2nd) by 8
56x + 49y = -105 (multiply 7)
-56x - 72y = -56 (multiply 8)
--------------------------------------------add
-23y = -161
y = 7
8x + 7y = -15
8x + 7(7) = -15
8x + 49 = -15
8x = -64
x = -8
answer
x = -8 and y = 7