So,
Your question has already provided the necessary information for us to be able to compute the volume. To find the volume of the triangular prism, you just need to multiply the area of the base (a triangle) by the height (15).
We already know how to find the area of a triangle.

5(4)
20 cm²
Now, multiply that by the height of the prism.
20 * 15 = 300 cm³
The volume of the triangular prism is 300 cm³.