Step-by-step explanation:
as we just learned a few minutes ago, the volume of a prism is
base area × height
the trick is to see that this prism is laying on its side !
the base area is a triangle.
we see here, it is a right-angled triangle that is also isoceles (both legs are equally long).
so, as explained in the other answer earlier, the area of that triangle is simply
leg² / 2 = 7.5²/2 = 28.125 ft²
and the volume of the prism is
28.125 × 10 = 281.25 ft³
