Answer:
The height of the triangular prism is
![26\ mm](https://img.qammunity.org/2020/formulas/mathematics/high-school/g3wloqxpx6mdfzj5jfg9x5ehkewm9y4yqn.png)
Explanation:
see the attached figure to better understand the problem
we know that
The volume of the triangular prism is equal to
![V=Bh](https://img.qammunity.org/2020/formulas/mathematics/college/1z8biyc5dxidzjd7gaahhzli35rckolci0.png)
where
B is the area of the triangular base
h is the height of the prism
Find the area of the base B
![B=(1)/(2)(7)(18)=63\ mm^(2)](https://img.qammunity.org/2020/formulas/mathematics/high-school/jmqadnariyiy3qx55ps1o7yisnzsk97kpy.png)
we have
![V=1,638\ mm^(3)](https://img.qammunity.org/2020/formulas/mathematics/high-school/sv08j4tfgnv8g2h86gaks2jnjqsdd25o8x.png)
![h=x\ mm](https://img.qammunity.org/2020/formulas/mathematics/high-school/cg1hp8a9ce5m867zzgy45k557zc5o7501x.png)
substitute and solve for x
![1,638=(63)x](https://img.qammunity.org/2020/formulas/mathematics/high-school/um85pqx41wa9u834aldaxhr9iwyzspz833.png)
![x=1,638/(63)=26\ mm](https://img.qammunity.org/2020/formulas/mathematics/high-school/fqtnthedbd3r8qb98ijyitko5vd8cob7ob.png)