The speed of the boat is 2 times the speed of the river. Find the speed of the boat if its speed along the river is 9 km / h.

Let’s make an equation in which we mark the speed of the river as an unknown speed x km / h.
In this case, since the speed of the boat is 2 times higher than the speed of the river flow, it will be: 2 * x km / h.
The sum of the current speed and the boat’s own speed will be equal to 9 km / h.
We get the following equation:
x + 2 * x = 9 km / h.
3 * x = 9.
x = 9/3.
x = 3 km / h – River flow speed.

Find the boat’s own speed.
To do this, replace x with 3 km / h.
We get:
2 * x = 2 * 3 = 6 km / h.