In Problem 25 - 28 find the volume of solid under the graph of each function over the given rectangle.
26.
f(x,y) = 5 - x;
R = {(x,y)}| 0 ≤ x ≤ 5, 0 ≤ y ≤ 2}
28.
f(x,y) = e-x-y;
R = {(x,y)}|0 ≤ x ≤ 1, 0 ≤ y ≤ 1}