The equation 17 + x = 21 represents the scenario below.
"Matteo spent a total of $21 on clothes. He purchased shirts and scarves. Matteo spent $17 on shirts."
What does the variable x represent in this scenario?
A. the amount of money Matteo spent on scarves
B. the amount of money Matteo spent on clothes
C. the number of shirts Matteo bought
D. the number of scarves Matteo bought