Welcome to PF;
... please explain your reasoning, and remember to include units in the answer.
I don't know what you mean by "(a)" in there. It looks like you are trying to calculate a force and you have noticed that you do not know the acceleration.
The work is the magnitude of the applied force multiplied by the distance moved in the direction of the applied force.
In the problem, you are told there is a "resistive" force - maybe that is the wind pushing on the object.
In order to move the object "against the wind", what is the minimum applied force that is needed?