The motor ship sailed along the current for 168 km in 6 hours. How long did it take for the return trip if the river speed was 2.8 km / h?

1) Let’s calculate the speed of the ship along the river. To do this, we divide the distance that he traveled by the time spent on this path:
168: 6 = 28 km / h.
2) Determine the own speed of the ship. To do this, subtract the speed of the river from its speed of movement along the current:
28 – 2.8 = 25.2 km / h.
3) To find out the speed of the motor ship against the current (on the way back), it is necessary to reduce its own speed by the speed of the river flow:
25.2 – 2.8 = 22.4 km / h.
4) Let’s calculate how long it will take for the ship on the way back:
168: 22.4 = 7.5 hours.
Answer: 7.5 hours