The cost of a pair of jeans is 4 times the cost of a book.
In this case, we want to write an expression representing the cost of the pair of jeans. The key phrase in the sentence is ... times ... This indicates that we should multiply two things.
... * ...
The two terms that are being multiplied are 4 and the cost of a book. Let b represent the cost of the book.
4 * b
Note that this is only one of the multiple ways to algebraically express the given verbal expression.
