Given: 30km upstream and downstream distance. Time taken is 16/5 hours. Speed of stream is 5 km/hr Formula Used: Speed = Distance/Time Speed in upstream direction = x – y Speed in downstream direction = x + y Where, x is speed of a boat in still water y is speed of a stream Calculation: According to the question, ⇒ 16/5 = 30/(x – y) + 30/x + y) ⇒ 16/5 = 30/(x – 5) + 30/(x + 5) ⇒ 16/5 = {30(x + 5) + 30(x – 5)}/(x – 5)(x + 5) ⇒ 16/5 = (30x + 150 + 30x – 150)/(x2 – 25) ⇒ 16/5 = 60x/(x2 – 25) ⇒ 4/5 = 15x/(x2 – 25) ⇒ 4(x2 – 25) = 5 × 15x ⇒ 4x2 – 100 = 75x ⇒ 4x2 – 75x – 100 = 0 ⇒ 4x2 – 80x + 5x – 100 = 0 ⇒ 4x(x – 20) + 5 (x – 20) = 0 ⇒ 4x + 5 = 0 or x – 20 = 0 ⇒ x = –5/4 or x = 20 Speed can not be negative, ⇒ x = 20 Upstream speed = x – y ⇒ Upstream speed = 20 – 5 ⇒ Upstream speed = 15km/hr To cover 144 km distance upstream, ⇒ Time = 144/15 ⇒ Time = 9.6 ∴ Time taken to cover 144 km distance is 9.6 hours.