How Do I Calculate Air Resistance Force with Vertical Acceleration?

[paperdoll]

If I know the theoretical acc down is 9.8 and I have the actual acceleration to be 9.2, do I use 9.8-9.2 to find the air resistance force? Or do I use 9.2-9.8?

And then after that, do I multiply it by the mass? Or do I calculate both forces and then subtract them?

 

[gneill]

As usual, draw a Free Body Diagram showing the forces acting...