Answer:
We can use the following equation to answer the question: d = (50 mph)(15 minutes/60 minutes) + (40 mph)(t minutes/60 minutes).
Where t is the total time it takes Alex to travel to the appointment. Solving for t, we get t = (d - 15 mph)/(10 mph).
Therefore, the appointment is d = (50 mph)(15 minutes/60 minutes) + (40 mph)(t minutes/60 minutes) = (750 miles/hr)t miles away from Alex's house.