In the first 240 miles, the car travel at the time:

240 : 60 = 4 (hrs)

In the next 160 miles, the car travel at the time:

160 : 80 = 2 (hrs)

The time remaining is: 9 - 4 - 2 = 3 (hrs)

The distance remaining is: 616 - 240 - 160 = 216 (miles)

The average speed of the car before the remainder of the trip in order for the car to arrive on schedule is: 216 : 3 = 72 (mph)

Lê Quốc Trần Anh selected this answer.