If the Total Surface Area of a Right Circular Cone $72 \pi$

Multiple Choice

If the total surface area of a right circular cone is $72 \pi$ square feet and a radius of the base is 6 feet long, find the slant height of the cone.

A) $4 \pi$ feet
B) $18$ feet
C) $6$ feet
D) $12$ feet
E) none of these