We have that the volume of a rectangular prism is given by the following expression:
[tex]V=l\cdot w\cdot h[/tex]
Here l is the length, w the width, and h the height.
Now, we replace the values:
[tex]V=(16)(12)(9)\Rightarrow V=1728[/tex]
So, she will need 1728 cubic inches of soil to fill the box completely.
