Anet force of 100 newtons is applied to a wagon for 5 seconds. this causes the wagon to undergo a change in momentum of

In this question, it is important to understand the trick that is hidden in it. Initially it might look that the problem is unsolvable, but it is definitely solvable. Now let us first write down all the information's that are provided.
Force = 100 Newtons
           = 100 kg m/s^2
Time = 5 seconds
Now we know the unit of momentum to be kg m/s. So if we multiply the time with momentum then we can get the momentum very easily.
Then
Momentum = (100 * 5) kg m/s
                   = 500 kg m/s
So the momentum of the wagon is 500 kg m/s

The independent variable would be the fertilizer as it is what the dependent variable (the growth of grass) depends on.