Answer
25 kilometers per hour 🎯
Any equivalent answer (such as meters per second) will also be accepted.
It is important to assume that the speed of the person (with or without the vehicle) and the influencing force (such as wind or water current) are constant (as in uniform motion), or most Math problems in general (not just from this mini-contest) would not have answers. It is like saying that a person running at 20 kilometers per hour for 5 hours won't reach 100 kilometers "because he got tired on the way and slowed down running" if data are "ever-changing" and not constant.
Solution
The original problem is similar to the one at @savvyplayer/math-mini-contest-problem-for-day-12-on-d-buzz which is under uniform motion word problems in (elementary) algebra.
Let j = speed of 
Let w = speed of the wind
Let t = time it takes to cover the distance
| Time | Rate | Distance | |
|---|---|---|---|
| with the wind | 2 | j + w | 300 |
| against the wind | 3 | j - w | 300 |
Remember that in distance problems, the distance is the result of the rate multiplied by the time.
Equation 1: 2 * (j + w) = 300
Equation 2: 3 * (j - w) = 300
We now have a system of linear equations in two variables. We should simplify Equations 1 and 2 before solving for the value of the variables.
Equation 3: j + w = 150
Equation 4: j - w = 100
We can now use the Elimination Method to get the value of w by subtracting Equation 4 from Equation 3.
(j + w) - (j - w) = 150 - 100
2j = 50
j = 25
Therefore, the speed of the wind is 25 kilometers per hour.
We can also get the speed of
RE: Math mini-contest problem for Day 18 on D.Buzz 😎