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 [tex]\frac{s^2\sqrt{3}}{4}[/tex], where s is the side-length, so in this case, the base area is [tex]\frac{81\sqrt{3}}{4}[/tex]. Now, we multiply by 12, the height, and divide by three (which is equivalent to multiplying by four overall), for a result of [tex]81\sqrt{3}[/tex]. To round to the nearest tenth, you'd generally need a calculator - using one, the answer is 140.3.
