Question 600257
He drove 5 hours at 55 mph. So he drove d = rt = 55*5 = 275 miles so far.


He now has 665 - 275 = 390 miles left to go


So d = 390. 


Since he wants to complete the trip in 11 hours, and he's already taken up 5 hours, he has 11 - 5 = 6 hours left. 


So t = 6


Now use d = rt to solve for r



d = rt


390 = r*6


390/6 = r


65 = r


r = 65


So he must average 65 mph