The volume of a triangular prism is the following equation:
[tex]V=Ah[/tex]
where A represents the area of the base and h represents the height of the prism.
In this case, the area of the base is the following:
[tex]A=\frac{12\cdot9}{2}=\frac{108}{2}=54yd^2[/tex]
then, the volume of the prism is:
[tex]V=54(20)=1080yd^3[/tex]
