<u>Answer:</u>
The total time taken to complete 25 miles is 7.6 hours.
Solution:
Ben walks 5 miles in 1 hour,
Second 5 miles in 1.4 hours,
Third 5 miles in 1.7 hours,
Last 5 miles in 1.8 hours
So he walked total 20 miles in (1+1.4+1.7+1.8) hours = 5.9 hours = 6 hours (approximately)
So his average speed is
miles/hours = 3.33 miles/hours.
i.e. he travels 3.3 miles in 1 hour,
Then, he travels 1 miles in
hours
Hence the total time he will take to walk 25 miles is 

That is approximately 7.57 or 7.6 hours.