Find the second partial derivatives of the function $\displaystyle f(x,y) = x^{4}y^5+6 x^{3}y.$

1. $\displaystyle \frac{\partial^2 f}{\partial x^2} =$

2. $\displaystyle \frac{\partial^2 f}{\partial y \partial x} =$

3. $\displaystyle \frac{\partial^2 f}{\partial x \partial y} =$

4. $\displaystyle \frac{\partial^2 f}{\partial y^2} =$