Let C be the positively oriented square with vertices $\left( 0, 0 \right)$, $\left( 1, 0 \right)$, $\left( 1, 1 \right)$, $\left( 0, 1 \right)$. Use Green's Theorem to evaluate the line integral $\int_{C} 3 y^{2} x \, dx + 6 x^{2} y \, dy$.