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?
Answer Choices
A. 18
B. 162
C. 36 \sqrt{21}
D. 18 \sqrt{138}
E. 54 \sqrt{21}