If 5x^2 + y^4 = -9 then evaluate the second derivative of y with respect to x (d^2y/dx^2) when x = 2 and y = 1. Round your answer to two decimal places.

I've tried this, but just can't seem to get it. Anyone think they can help? I can get as far as knowing the derivatives 10x and 4y^3, but from there I'm quite lost. If you don't mind explaining the process of the problem as well, that'd be appreciated. Thank you!