How should I evaluate $\left(\frac{\partial U}{\partial V}\right)_T$ with van der waals equation: $P = \frac{nRT}{V-nb}-a(\frac{n}{V})^2$?

So in my homework I was able to get this-


$\left(\frac{\partial U}{\partial V}\right)\_T = T(\frac{\partial P}{\partial T})\_V - P$


but now I'm trying to plug in $P = \frac{nRT}{V-nb}-a(\frac{n}{V})^2$ in the above equation. I'm struggling here, I got zero for
$\left(\frac{\partial U}{\partial V}\right)\_T$ but I'm then asked to evaluate $\left(\frac{\partial U}{\partial V}\right)\_T$ in an integral from infinity to $V$ with respect to $V$ (i.e. $dV$).


