Answer:
200N
Step-by-step explanation:
The net force or resultant force on the object is obtained by adding all the forces acting on it.
In this case we have an upward force and a downward force, since they go in different directions they must have a different sign: we will define upward as positive and downward as negative:
![F_(air) = 400N](https://img.qammunity.org/2020/formulas/physics/middle-school/9r71t2zwnha170wit6m473g0cmndn75twf.png)
![F_(grav)=-600N](https://img.qammunity.org/2020/formulas/physics/middle-school/mqlz5i94lkkh4hy72kqoisyqkk1osbyc7h.png)
The sign only to indicate that they are going in opposite directions, so the resulting force:
![F=F_(air)+F_(grav)=400N+(-600N)=400N-600N=-200N](https://img.qammunity.org/2020/formulas/physics/middle-school/jbi7fuk6o94tyh2kyrlhlpcql23dwfc1f1.png)
The net force acting on the object is 200N. (downwars due to the negative sign).