Pyramid Surface Area = (½ * Perimeter of Base * Slant Height) + Base Area
Base perimeter = 4 * 18 = 72 inches
Base Area = 18*18 = 324 square inches
Pyramid Surface Area = (.5 * 72 * 12) + 324
Pyramid Surface Area = 432 + 324
Pyramid Surface Area = 756 square inches
Source:
http://www.1728.org/volpyrmd.htm
