We have a rectangular prism.
In general, for any prism, the next expression is valid:
Where A is the area of the base and h is the height
So, first, we need to calculate the area of the base. As it is a rectangle, we know that the area is given by:
Then, based on the figure: DBB=9in
Finally, we use the formula that is actually already expressed in the document (Notice that, in this case, h=DBB, A=AB)
As for the last step, we need to round to the nearest hundredth. This is unnecessary as we are working with whole numbers