23) Determine whether F(x, y) = (x y', xy") is conservative. If it is, find a potential function f(x, y) and use it to evaluate w = J F . dr along the curve C: r(t ) = (t3 - 21, t3 + 2t) for 0 c t = 1, 24) Use Green's Theorem to calculate o, yet dx + 2edy where C is the rectangle with vertices (0,0), (3,0), (3,4). and (0,4)