Answer:
Step-by-step explanation:
If all faces are equilateral, and they are all congruent, that means the surface area of the pyramid is formed by 4 equal triangles, including the base.
We just need to find the area of one triangle and then multiply it by 4.
According to the image, the height of a triangle face is [tex]h=7.8 \ ft[/tex], and its base is [tex]b=9 \ ft[/tex]. So, the area is
[tex]A=\frac{1}{2} (b \times h)[/tex]
[tex]A=\frac{1}{2}(7.8 \times 9) =35.1 \ ft^{2}[/tex]
Then, the total surface area of the pyramid is
[tex]S=4(35.1)=140.4 \ ft^{2}[/tex]
Therefore, the right answer is B. 140.4 square feet.
