Write a double integral that represents the surface area of z = (x, y) over the region

Write a double integral that represents the surface area of z = ƒ(x, y) over the region R. Use a computer algebra system to evaluate the double integral.

ƒ(x, y) = x² + y², R = {(x, y): 0 ≤ ƒ(x, y) ≤ 16}