x = -2, y = -1
Substitution method:
2x + 3y = -7
y = 8x + 15
2x + 3(8x + 15) = -7
2x + 24x + 45 = -7
26x = -52
x = -2
Substituting x value back into 1st equation for y:
2(-2) + 3y = -7
3y = -3
y = -1
