Answer :
-- Ben walks at a rate of 3 miles per hour. If he walks for 'W' hours,
then the distance he covers in that time is 3W miles.
-- Ben runs at a rate of 6 miles per hour. If he runs for 'R' hours,
then the distance he covers in that time is 6R miles.
If he does some running and some walking during the week, then
we might not know how many hours he walked and how many hours
he ran, but we can be sure that the total distance he covered is
Total D = 3W + 6R .
-- If the total distance is 210 miles,and he ran for 25 hours, then
210 = 3W + 6(25)
210 = 3W + 150
Subtract 150 from each side: 60 = 3W
Divide each side by 3 : 20 = W
He walked for 20 hours during the week.
Check:
Running hours: R=25, Running D = 6R = 150 miles.
Walking hours: W = 20, Walking D = 3W = 60 miles.
Total distance = 150 miles + 60 miles = 210 miles yay !