The volume of a prism is area of the base times height.
This is a triangular prism. The base is a triangle.
The volume is area of the base times height, and the base is a triangle.
Find the area of the triangle and multiply by the height of the prism.
V = volume of the prism
A = area of the base
H = height of the prism
h = height of the triangle
b = base of the triangle
V = AH
V = (1/2)bhH
V = (1/2) * 9 ft * 7 ft * 15 ft
V = 472.5 ft^3