If the difference between the speed of boat M in still water and the speed of stream is 15 kmph and the speed of the boat P is 40% less than the speed of boat N in still water. The time taken by boat N to cover x km along with stream is 6 hours and boat M covers the same distance along with stream in 7.2 hours and boat P covers 160 km along with stream in 8 hours. If the time taken by boat M to cover (x + y) km against the stream is 7.6 hours more than the time taken by boat N to cover x km along with stream. Find the value of y.