Answer:
t = 9in
Explanation:
The formula of a volume of a prism:
![V=BH](https://img.qammunity.org/2020/formulas/mathematics/middle-school/5cp42nuplbh6iz7ybq2kknco2ra5umr2p2.png)
B - area of a base
H - height
In the base is the triangle.
The formula of an area of a triangle:
![A=(bh)/(2)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/ldsjq5pl6s8nfwkzzwkdtmhxkudpyw69zw.png)
b - base
h - height
We have V = 247.5 in³, b = 5 in, H = 11 in and h = t.
Therefore:
![B=(5t)/(2)](https://img.qammunity.org/2020/formulas/mathematics/high-school/1jjra0n8zseykpasvisdpp6ecz4v2sd14m.png)
Put them to the formula of a volume:
![247.5=\left((5t)/(2)\right)(11)](https://img.qammunity.org/2020/formulas/mathematics/high-school/5qaxl7g8jzmnhm9zw02lbfjjgon3timgb9.png)
![247.5=(55t)/(2)](https://img.qammunity.org/2020/formulas/mathematics/high-school/7ipbux4ifkovryihq1771i2xmocsrhkznx.png)
divide both sides by 27.5
![9=t\to t=9\ in](https://img.qammunity.org/2020/formulas/mathematics/high-school/hr2yv6a74a38bo3a4kiyzpevye7l2baabj.png)