20,30,13,10,14,10,10,?,?,?

Can some one me with these questions

We just started the introduction into circles and i have no idea how to do this.

Use stokes' theorem to evaluate c f · dr where c is oriented counterclockwise as viewed from above. f(x, y, z) = xyi + 5zj + 7yk, c is the curve of intersection of the plane x + z = 8 and the cylinder x2 + y2 = 81.