Answer:
t = 9in
Explanation:
The formula of a volume of a prism:

B - area of a base
H - height
In the base is the triangle.
The formula of an area of a triangle:

b - base
h - height
We have V = 247.5 in³, b = 5 in, H = 11 in and h = t.
Therefore:

Put them to the formula of a volume:


divide both sides by 27.5
