Solution:

$$ \begin{aligned} u &=x^{3}+3 x^{2} y+3 x y^{2}+y^{3}.....(A) \\\\ \frac{\partial u}{\partial x} &=3 x^{2}+6 x y+3 y^{2}+0 \\\\ x \frac{\partial u}{\partial x} &=x\left(3 x^{2}+6 x y+3 y^{2}\right) \\\\ x \frac{\partial u}{\partial x} &=3 x^{3}+6 x^{2} y+3 x y^{2}........(1) \\\\ u &=x^{3}+3 x^{2} y+3 x y^{2}+y^{3} \\\\ \frac{\partial u}{\partial y} …