Evaluate the surface integral F. ds for the given vector field F and the oriented surface S. In other words, find the flux of F across S. For closed surfaces, use the positive (outward) orientation. 33x 2 F(x, y, z) = -xi-yj+k, S is the part of the cone z = x2+y2 between the planes z = 1 and z = 2 with downward orientation