EXPLANATION:
The volume of a rectangular prism is given by the formula
[tex]\begin{gathered} \text{Volume}=\text{length}\times Breadth\times Height \\ or \\ \text{Volume}=\text{Base Area }\times Height \end{gathered}[/tex]The values will be:
[tex]\begin{gathered} \text{Base Area =}18\times15=270\text{inches}^2 \\ \text{Height}=20\text{inches} \end{gathered}[/tex]Thus, the volume of the prism is
[tex]\begin{gathered} \text{Volume}=270\times20 \\ \text{Volume}=5400inches^3 \end{gathered}[/tex]Thus, the answer is 5400 inches³