Let the speed of the boat in still water be $5s$ km/h. The speed of the stream is $\frac{4}{5} \times 5s = 4s$ km/h. - The downstream speed is the sum of the boat speed and stream speed: $5s + 4s = 9s$ km/h. - The downstream distance is 198 km, covered in 11 hours. Therefore: \[9s = \frac{198}{11} = 18 \implies s = 2\] - Consequently, Boat speed = $5s = 10$ km/h, Stream speed = $4s = 8$ km/h. - The upstream speed is the difference between the boat speed and stream speed: $10 - 8 = 2$ km/h. - The time required to travel 60 km upstream is $\frac{60}{2} = 30$ hours. - The time required to travel 36 km downstream is $\frac{36}{10+8} = \frac{36}{18} = 2$ hours. - The difference in time is $30 - 2 = 28$ hours.