Stuck on this problem

[shawonna23]

A rock of mass 33 kg accidentally breaks loose from the edge of a cliff and falls straight down. The magnitude of the air resistance that opposes its downward motion is 239 N. What is the magnitude of the acceleration of the rock?

I tried a=239*33 and I got 7.24 but that was wrong. Please help. I don't know what else to do.

[Pyrrhus]

What are the forces acting on the block?

What does newton's 2nd law state?

[faust9]

Did you draw a free body diagram of the falling rock including all forces acting upon the rock?

Did you write out \sum \vec F=m\vec a? I'm sure if you do the above and sum the forces you'll get the correct answer.