Find d^2/dx^2 (second derivative) if y^2+2y=4x^2+2x.

The first derivative is 4x+1/y+1. Now, when I get to 4(y+1)-(4x+1)(4x+1/y+1) / (y+1)^2, I'm stuck. My book says the answer is 4(y+1)^2-(4x+1)^2 / (y+1)^3 is the answer... how do you get that answer? What must you do? And why does the denominator increase by a power?

Thank you for your help