Niles and Bob sailed at the same time for the same length of time. Niles' sailboat traveled 15 miles at a speed of 5 mph, while Bob's motorboat traveled 42 miles at a speed of 14 mph. For how long were Niles and Bob traveling?

7 MPH

Explanation:

the speed of the river is c=mph

The effective downstream speed = 14 + c

The effective upstream speed = 14 - c

Total time = 4 hrs

Total distance = 42 miles

Time for upstream + time for downstream = 4 hrs

21 / (14 + c) + 21 / (14 - c) = 4

21 (14 - c + 14 + c) = 4 (196 - c^2)

21 x 28 = 4 (196 - c^2)

c^2 = 196 -147 = 49

C=7 mph hope this helps

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