Use Green's Theorem to evaluate the following line integral.\\
$\oint_C f dy - g dx$, where $(f,g) = (3x^2, 6y^2)$ and $C$ is the upper half of the unit circle and the line segment $-1 \le x \le 1$ oriented clockwise.\\
$\oint_C f dy - g dx = $\\
(Type an exact answer, using $\pi$ as needed.)
