The problem is:
Find all functions $f(x,y)$ such that:
$f(x,y){(1 - 3x^2)} = {(x^3 + y^2)}{(\frac{\partial f}{\partial x}} (x,y)) - {(x^2 + y)} {(\frac{\partial f}{\partial y}} (x,y))$
I am not being able to think the first step to proceed with the problem. Please help me.