I need to find the second derivative for this:

2x^2-3y^2=4
I understand all the steps but for some reason I get the wrong numerator. I get
(6y^-4x^2)/9y^3
The answer is -8/9y^3

The original equation says that 4x^2-6y^2=8. So, your answer is correct, but unsimplified.