Since the foil covers the object and does not fill it, this problem is a matter of surface area rather than volume. Surface area is finding the area of all the faces, and adding them up.
Since we know the two triangular ends are not covered, this actually makes the problem easier.
Going with our definition of surface area above, we do:
You need to calculate and add the surface area of the three rectangular faces of this prism. The two triangular ends are not covered in the foil as stated in the question. You find this like any other rectangle by multiplying the length by the width. (a = lw)
Let's start with the bottom rectangle, it has dimensions of 5x 16.5ft