Answer: 60 miles
Step-by-step explanation:
Let x denote the distance between his home and the place of appointment and t be the time taken by him at 40 mph.
Also, 

Since he left the house 15 minutes late, he drove the car at 50 mph and arrive 3 minutes early for the appointment.
15 minutes=
3 minutes=
Then actual time taken by him =t-0.25-0.05=t-0.30

From (1) and (2), we have

Put the value of t in (1), we get

Hence, the distance between his home and the place of appointment = 60 miles.