To solve this problem you must apply the proccedure shown below:
1. You can use the following formula for calculate the volume:
![V=((a+b)/(2))(h)(l)](https://img.qammunity.org/2019/formulas/mathematics/high-school/5me86ewuqxevjq8uarpfe5x5m85wys35ug.png)
Where:
![a=6m\\b=12m\\h=8m\\l=3m](https://img.qammunity.org/2019/formulas/mathematics/high-school/3sec9lfgyhvlb20ok71lho8u50aohyushh.png)
2. Now, you must substitute the values above into the formula:
![V=((a+b)/(2))(h)(l)\\V=((6m+12m)/(2))(8m)(3m)\\V=216m^(3)](https://img.qammunity.org/2019/formulas/mathematics/high-school/dp0ltali31x0y8d56vvrccuu6rgt5mjfnm.png)
Therefore, the answer is the last option: D. 216 m³.