Circles with centers at O and P have radii 2 and 4 , respectively, and are externally tangent. Points A and B on the circle with center O and points C and D on the circle with center P are such that \overline{A D} and \overline{B C} are common external tangents to the circles. What is the area of the concave hexagon A O B C P D ?
Answer Choices
A. 18 \sqrt{3}
B. 24 \sqrt{2}
C. 36
D. 24 \sqrt{3}
E. 32 \sqrt{2}