Distance = Speed x time
For the run; speed = 5 mi/hr, time = t
For the walk: speed= 2 mi/hr, time = t + 1
Since he walked on a straight line and he returned following the same path
Distance travelled for the run = distance travelled for the walk
Distance for run: 5 x t = 5t
Distance for walk : 2 (t + 1) =2t + 2
Thus , 5t = 2t + 2
5t - 2t = 2
3t = 2
t = 2/3 hour = 2/3 x 60 minutes = 2x 20 = 40 minutes
He took him 40 minutes to run