Use Stokes' Theorem to evaluate F . dr, where F = (-yz, 4y + 1, xy) and C is the circle of radius 3 at y = 4 and perpendicular to the y-axis. Looking at C from the positive y-axis to the negative y-axis, C has clockwise orientation. Hint: Think of using the appropriate elliptic paraboloid for the surface, since this will give the easiest integral