The distance between A and B is 205 km. One boat starts moving from A towards B in downstream at 8:15 am. After one hour, another boat starts from B towards A. Both the boats meet at 02:15 pm. If speed of first and second boat in still water is 21 km/hr and 15 km/hr respectively, then find the speed of current.

14 km/hr

Let the speed of current be s km/hr

Distance covered by first boat in 1 hour = (21 + s) km

Distance between two boats becomes=  205 - (21 + s) at 09:15am

Relative speed of two boats = (21 + s) - (15 - s) = 2s + 6

(Since, the second boat will travel upstream)

Distance = Speed x time 

⇒ 205 - (21 + s) = (2s + 6) x 5

⇒ 184 - s = 10s + 30

⇒ 11 s = 154

   s = 14