Two boats A and B start towards each other from two places, 108 km apart. Speed of the boats A and B in still water are 12 km/h and 15 km/h respectively. If A proceeds down and B up the stream, they will meet after:

Explanation:-

Let the speed of the stream be x kmph and both the boats meet after t hour.

According to the question,
(12+x)*t+(15-x)*t = 108;
Or, 12t+15t = 108;
Or, 27t = 108;
Or, ¹⁰⁸/₂₇ = 4 hours.