The answer is 52 if you are looking for the answer to 2x2x13=? then it is 52. Otherwise idk what you are asking.
First lets get the formula for a triangular prism

First lets plug in our numbers

It really doesnt matter how you multiply everything, but you end up with 119cubic feet.
An explicit equation is an equation used to find a term in a sequence without using the any previous terms. For example, if I have the set of numbers 1, 3, 5, 7, 9, my explicit equation is F(n)=2(n-1)+1. If I plug 1 in for n, I get F(1)= 2(0)+1, which is 1, my first term.
Hope this made sense.