AMC 12 2015b Problem 16

A regular hexagon with sides of length 6 has an isosceles triangle attached to each side. Each of these triangles has two sides of length 8. The isosceles triangles are folded to make a pyramid with the hexagon as the base of the pyramid. What is the volume of the pyramid?

\textbf{(A)} 18 \textbf{(B)} 162 \textbf{(C)} 36\sqrt{21} \textbf{(D)} 18\sqrt{138} \textbf{(E)} 54\sqrt{21}