This problem is based on Example #1 in §12.1 of Stewart (pg 833).
Estimate the volume of the solid that lies above the square R=[0,2]×[0,2]\displaystyle {R}={\left[{0},{2}\right]}\times{\left[{0},{2}\right]} and below the elliptic parabolid z=15.8x22.1y2\displaystyle {z}={15.8}-{x}^{{2}}-{2.1}{y}^{{2}}. Divide R\displaystyle {R} into four equal squares and choose the sample point to be the upper right corner of each square Rij\displaystyle {R}_{{{i}{j}}}. For your own benefit, you should consider sketching the solid and the approximating recatngular boxes.

Approximate volume = units³.