A boat travels from point 'Y' to point 'Z' downstream and then returns to point 'X', which is located midway between 'Z' and 'Y'. The entire trip takes 11 hours. The distance between points 'Y' and 'Z' is 150 km. If the boat's speed in still water is three times the speed of the stream, determine how long it will take the boat to travel 180 km upstream.