A motorboat maintained a constant speed of 15 miles per hour relative to the water in going 10 miles upstream and then returning. The total time for the trip was 1.5 hours. Find the speed of the current.

Let c = current's speed

Distance is given to be 10 miles.

D = rt is manipulated to be t = D/r.

[10/(c - 15)] + [10/(c - 15) = 1.5

Is this correct?