The speed of the river is 2 km / h. How long does it take for a boat to cover 30 km downstream

The speed of the river is 2 km / h. How long does it take for a boat to cover 30 km downstream if it covers this distance upstream in 5 hours?

Let X be the speed of the boat when there is no current.
The speed of the boat against the current will be equal to the difference between the speeds of the boat and the current: X – 2.
Let’s make the equation:
5 * (X – 2) = 30
5 * X – 10 = 30
5 * X = 40
X = 40/5
X = 8 km / h
The speed of the boat downstream will be equal to the sum of their speeds: X + 2 = 8 + 2 = 10 km / h, so it will go all the way in 30/10 = 3 hours.