I NEED HELP ASAP, THIS IS MY LAST QUESTION FOR MY TEST!!!!!!

at a book fair, Scott bought a 4$ tote bag and some books for 2$ each. The total amount Scott spent is represented by the equation below.

y= 2x + 4

what does the variable x represent in this equation?
A. the cost for one book
B. The total amount spent
C. the number of books bought
D. the cost of all the books bought