Compute the volume of each of the following regions.
a) E is bounded by the surfaces x + y + z = 3, z = 0, and x2 + y2 = 1.
b) E lies under the plane z = x + y and over the region in the xy-plane bounded by the curves x = √y/2, x = 2√y, x + y = 3.
c) E is bounded by z = y2, x = y2 + z2, x = 0, z = 1.
d) E is bounded by y = x3, x = z2, z = x2, and y = 0.