Let $R = [0,4] \times [-1,2]$. Create a Riemann sum by subdividing $[0,4]$ into $m=2$ intervals, and $[-1,2]$ into $n=3$ subintervals, then use it to estimate the value of $$\iint_R \! \left(1-xy^2\right)dA.$$ Take the sample points to be the upper left corner of each rectangle.

Answer: