How do I find the function of x

Hi, please click on the attachment and help me with finding the function of x.

Thanks.

Notice that sqrt(x) squared is x. So if you write t = sqrt(x), your equation is t^2 - 7t - 8, which is a quadratic equation in t. Solve it to get t = -1 or 8 and then find x = 1 or 64.

Thanks for the help. This seems to be a better approach than my book.