Please help and if possible show your work

Answer:
514.5 ft.³
Step-by-step explanation:
Volume of a triangular prism
= base area × height
In the figure, the base is a right-angled triangle.
The base area
= (7×7)÷2
= 24.5 ft²
The volume of the prism
= 24.5×21
= 514.5 ft³