A boat can cover X km while going downstream in same time in which it can cover (X-8) km while going up stream. If the difference between the distance covered in 1 hr. Downstream and upstream is 6 km and speed of boat in still water is 15 km/hr, then find the value of X.

Let stream speed = s km/hr. Downstream speed = 15+s, upstream = 15-s. In equal time t: distance downstream = (15+s)t = X, distance upstream = (15-s)t = X-8. Difference in 1 hour: (15+s) - (15-s) = 2s = 6, so s = 3. From the equations: X/(15+3) = (X-8)/(15-3), giving X/18 = (X-8)/12. Cross-multiply: 12X = 18X - 144, so 6X = 144, X = 24 km.