(6 points) 3. Estimate / f,(3xy' + 2x2) dA where R = [0, 1] x [0, 1] by dividing R into four equal squares and evaluating the function at the upper right corner of each square. (7 points) 4. Find the volume under the surface z = 1 + o y and above the region in the xy-plane enclosed by the parabola = y- and the line r =4