Geometry

Question Analysis
This question involves the application of the basic combination formula for non - repetitive selection.
The main focus is on correctly using the formula by identifying (total number of books) and (number of books to display), and performing the factorial calculations accurately.

Key Concept Explanation
The formula is used to find the number of ways to choose distinct items from items when the order of selection does not affect the result.
In this case, the order in which the books are placed in the showcase does not matter, so combinations are applicable.

Step - by - Step Solution
First, calculate the factorials: