A boat takes 12 hours to cover a distance of 180km in downstream,while still in water ,it takes 8 hrs more.find out time taken by boat to over a distance of 72km upstream?

Let the speed of the boat in still water be x km/hr and the speed of the stream be y km/hr.

Downstream speed = (x + y) km/hr
Upstream speed = (x - y) km/hr

Given that the boat takes 12 hours to cover 180 km downstream:
180 / (x + y) = 12
x + y = 15

Given that the boat takes 8 hours more to cover the same distance in still water:
180 / x = 20
x = 9

Substitute x = 9 into x + y = 15 to find y:
9 + y = 15
y = 6

Now, to find the time taken by the boat to cover a distance of 72 km upstream:
72 / (9 - 6) = 24

Therefore, the boat takes 24 hours to cover a distance of 72 km upstream.