Answer:
A. 311.4
Step-by-step explanation:
The surface area of a 3D figure is simply the sum of the areas of all the exterior surfaces.
Here, the pyramid has a square base with dimensions 9 ft by 9 ft, as well as four lateral isosceles triangles.
The area of a square is denoted by A = s², where s is the side length. Here, the side length is 9, so:
A = s²
A = 9² = 81 ft²
We know that the height of the triangle is 12.8 and the base is 9. Use the area formula of a triangle, which is A = (1/2) * bh, where b is the base and h is the height:
A = (1/2) * bh
A = (1/2) * 9 * 12.8 = 57.6 ft²
Since there are four of these triangles, multiply 57.6 by 4:
57.6 * 4 = 230.4 ft²
Finally, add 230.4 to 81:
81 + 230.4 = 311.4 ft²
The answer is thus A.
<em>~ an aesthetics lover</em>
