Solve the system equations
y=x^2-8 4x+y=-8

Insert y in the second equation and solve for x: 

4x+(x^2-8)=-8
4x+x^2-8=-8
4x+x^2=0
x^2+4x=0

x = -4

Now you insers this x-value in the first or second equation (i use the first): 
y=(-4)^2-8=16-8=8

Therefore the conclusion must be x=-4 and y=8