**Estimate the volume of the solid that lies below the surface z = xy and above the following rectangle.**

**R = (x, y) | 6 ≤ x ≤ 12, 4 ≤ y ≤ 8**

**(a) Use a Riemann sum with m = 3, n = 2, and take the sample point to be the upper right corner of each square.**

**Answer:**