The motor ship goes down the river. What is the speed of the ship if the speed of the river is 4 km / h

The motor ship goes down the river. What is the speed of the ship if the speed of the river is 4 km / h, and the own speed of the ship (the speed of standing water) is 21 km / h?

In the event that a motor ship moves down the river, it means that it follows the course of the river, since the flow of water moves from the source to the mouth (lake, sea, reservoir or other river).
In order to determine the speed of the ship along the river, you need to use the following formula.
V = V1 + V2,
Where:
V is the speed of the ship along the river;
V1 – own speed of the ship;
V2 is the speed of the river.
Let’s substitute the values from the condition into the formula.
V = 21 + 4 = 25 km / h.
Answer: the speed of the ship is 25 km / h.