An office furniture manufacturer that makes modular storage
files offers its customers two choices for the base and four choices
for the top, and the modular storage files come in five different
heights. The customer may choose any combination of the five
different-sized modules so that the finished file has a base, a top,
and one, two, three, four, five, or six storage modules.
How many choices does the customer have if the completed file
has four storage modules, a top, and a base? The order in which the
four modules are stacked is irrelevant.
The Answer in the appendix is 560.
I found a solution which had 5-1+4C4 (4) (2) = 560. I do not understand the terms. Why is it 5-1+4C4?