what exactly do you want here?
I guess it is simplifying the expression:

STEP - BY - STEP EXPLANATION
What to find?
An expression for the total number of books.
Given:
Number of shelves = 5
Number of books in each shelf = k
If Lucy has a bookcase with 5 shelves and each of this
shelf has k books, then the total number of books can be determine by multiplying the numbers of book by the numbers of shelves.
That is;

ANSWER
5K
His answer should be a square because a square is a parallelogram with four similar sides and four right angles. A quadrilateral is a square<span> if its a rhombus and/or rectangle.</span>