A pizza delivery worker purchased a used motor scooter that had been driven 12100 miles. He drives the motor scooter only on days he is working, during which he drives an average of 50 miles per day. After d days of pizza delivery, the motor scooter has been driven a total of 25000 miles. Which of the following equations best models this situation?
A. 50 (12100 + d) = 25000
B. (12100 + d) 50 = 25000
C. 12100d + 50 = 25000
D. 12100 + 50d = 25000