Answer:the formula to calculate average speed is :
average speed= total distance/elapsed time .
He drives 5 hours at 55 mph so we need to calculate first how far or the distance he has driven at the moment hence from the above formula d= rt ( r stand for speed and t stand for time while d stand for the distance)
d=rt
d= 55*5= 275 mph this is how far he has driven at the moment.
So to see how many miles left we subtract the miles he has covered to the total miles he has to cover ;
d =665-275= 390
He also want to cover this trip in 11 hours but he has already driven for 5 hours hence time= 11 - 5 = 6 hours left
So now we have d= 390 and t = 6
So now using the same formula we now need to find the average speed which is ' r' in the formula
d = rt
390=r*6
390/6=r
r = 65mph
hence he will have to drive 65 mph to complete his trip in 11 hours.
