"identify the volume of a regular triangular pyramid with base edge length 9 ft and height 12 ft. round to the nearest tenth, if necessary."

i keep on getting 108 ft., but isn't the correct answer.

The area of any pyramid is the base area multiplied by the height and divided by three.

The base of a regular triangular pyramid is an equilateral triangle.  The formula for the area of an equilateral triangle is , where s is the side-length, so in this case, the base area is .  Now, we multiply by 12, the height, and divide by three (which is equivalent to multiplying by four overall), for a result of .  To round to the nearest tenth, you'd generally need a calculator - using one, the answer is 140.3.