4. Let F(x, y, z) = (4x, 4y, 4z). (a) (5 pts) Find the flux of F across S1 where S1 is the surface defined by a2 + + 2 = 4 and y 2 0, oriented with the normal vector pointing in the positive y-direction. (b) (5 pts) Find the flux of F across S2 where S2 is the surface defined by x2 + 22