It would be 2.9 hours because you would add 4 of the 39 minute intervals together and for the last interval if Brian ran extra 2 miles which would be 20 miles. You would have to divide the 39 minute interval by 2 since he ran an extra 2 miles to get 19.5 minutes for him to get his last 2 miles for his 18 mile jog. Then add the 4 intervals of 39 minutes along with the 19.5 minutes to get you a total of 175.5 minutes and if you were to convert that to hours and minutes it would be 2 hours and 55 1/2 minutes so technically it would be 2.9 hours. To find the 2.9 you would divided 175.5 by 60 since there is 60 minutes an hour to get the answer 2.925 unrounded, but rounded it would get you the final answer 2.9 hours.
