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

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.