How is this problem solved

Someone . me. compound probability

Find an bif a = {3, 6, 9, 12) and b = {2, 4, 6, 8, 10).

Solve the problem by making up an equation. a man could arrive on time for an appointment if he drove the car at 40 mph; however, since he left the house 15 minutes late, he drove the car at 50 mph and arrive 3 minutes early for the appointment. how far from his house was his appointment?