For each of the following, evaluate ∫E f dV.
a) f(x, y) = (1 + x2)-1 and E is bounded by x = 1, y = 0, and y = x3.
b) f(x, y) = x + y and E is the triangle with vertices (0, 0), (0, 1), and (2, 0).
c) f(x. y) = x2exy and E is the triangle with vertices (0, 0), (1, 0), and(l, 1).
d) f(x, y, z) = x and E is the set of points (x, y, z) such that 0 < z < 1 - x2, 0 < y < x2 + z2, and x > 0.