e friend sitting on the swing = 50 kg
Rate of acceleration = 4 m/s^2
The above information's are already given in the question. We need to utilize these information's in such a manner that the answer to the question can be determined easily.
We already know that
Force = Mass * acceleration.
This formula has to be used to find the force exerted.
Then
Force exerted = Mass of the friend * Acceleration
= (50 * 4) kg m/s^2
= 200 Newton
So the force exerted by me is 200 Newton. I hope the explanation and the procedure is clear to you and you are satisfied with it.