The base of a triangular prism is the area of the triangle.
The area of a triangle is:
A = 1/2bh
where b is base and h is height
Here, our b is 8in, and our height is 3in.
Plug this into the Area formula:
A = 1/2 (8) (3)
A = 4 • 3
A = 12 inches squared
Hope this helped!