Finding the vertical force?

Homework Statement

Fireman weighs 100kg. He slides down a vertical pole with acceleration 3.0ms^-2.

a) Magnitude and direction of vertical force exerted by the pole on fireman?

f=ma

The Attempt at a Solution

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f=ma
f=100(3.0)
f=300N vertically up.

But the answer says that it is actually 680N vertically up, and I do understand how they came to this conclusion.
Can you please explain where to go beyond this point? Or point out a mistake I may have made? Thank you.

I also replaced with acceleration with gravity, which did not work.

billy_joule
Your relevant equation is more correctly stated as:
∑F=ma

That is, the sum of all forces are equal to ma.
You found the net force from the firemans mass and acceleration, but you aren't asked for the net force, you are asked only for the force the pole exerts on the man.

What other force acts on the fireman?
What is it's magnitude? Can you use this information to solve for the poles force?

haruspex