Strong form of flux conservation law with given flux and source

[kgottsch]

1. The flux of a conserved quantity can be written
q(x) = -x² (du/dx)-u
If the source term is f(x) = x, write the strong form of the conservation law.

I know the form of the strong form is : d/dx(c du/dx)+f(x)=0

I have no idea where to begin for this problem. The examples my professor gave us in class don't help at all. I've tried searching elsewhere online for a better explanation, with no luck.
Please help
Thanks

 

[kgottsch]

Anyone? I still have no idea where to even start.