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