ANSWER
40 meters per minute
Step-by-step explanation
We have to find the rate of the wind - in other words, the speed of the wind.
We know that the duck can fly 2400 m in 10 minutes with the wind, so the speed of the duck when it is flying with the wind is,
However, when the duck is flying against the wind, it can only fly 2/3 of this distance in the same time, which is,
So, the speed of the duck against the wind is,
The speed of the duck with the wind is the sum of the actual speed of the duck and the speed of the wind,
While the speed of the duck against the wind is the actual speed of the duck minus the speed of the wind,
If we subtract the equation of the speed against the wind from the equation of the speed with the wind, we have,
Solving for the speed of the wind and replacing the values,
Hence, the speed (or rate) of the wind is 40 meters per minute.