11-16. Stokes' Theorem for evaluating line integrals. Evaluate the line integral $oint_c F cdot dr$ by evaluating the surface integral in Stokes' Theorem with an appropriate choice of $S$. Assume that $C$ has a counterclockwise orientation.
11. $F = langle 2y, -z, x
angle$; $C$ is the circle $x^2 + y^2 = 12$ in the plane $z = 0$.
12. $F = langle y, xz, -y
angle$; $C$ is the ellipse $x^2 + y^2/4 = 1$ in the plane $z = 1$.