Region S lies in the first quadrant and is bounded by the polar curve r=4cosθ, the x-axis, and the y-axis. Computing its area in polar form or by the rectangular description 0≤x≤4 and 0≤y≤4x−x2 yields the same value. Which of the following is that value?
a) 38π
b) 4π
c) 2π
d) π