The problem is h(x) = x^2 + 8x

I know the domain is all real. But did I solve for x correctly?

I have set up the problem:

y = x^2 + 8x

y = x(x + 8)

y/x = x + 8

y/x - 8 = x

y-8 = x^2

x = square root y - 8

But I don't get how they got the answer of x is greater than or equal to -16. Please help me.