(a) Estimate the volume of the solid that lies below the surface z = xy and above the following rectangle. R = {(x, y) 16 ≤ x ≤ 12, 8 ≤ys ≤ 12} Use a Riemann sum with m = 3, n = 2, and take the sample point to be the upper right corner of each square. 1452 (b) Use the Midpoint Rule to estimate the volume of the solid in part (a). V = V = = 1452 ×