A rental car agency charges $38 per day plus $0.21 for each mile driven. Sandra paid $88.40 for renting a car from them for one day.Which of the following could be used to find the number of miles she drove that day?
A. 0.21x = 88.4
B. 38x + 0.21 = 88.4
C. 0.21x + 38 = 88.4
D. 38x + 0.21 (88.4)