The C in the forumla referes to the Capacity Usually measured in Mah (milli amp hours)

Here is an example my charger uses Amps to measure its output

To fast charge my 300mah Nimh pach at 2C (most people agree that charging NiMh packs at more then 2C is not a good thing) the charger needs to be at:

Formula 2(300) /1000 = .6 amps

you Divide by 1000 to convert to amps

BTW I'm not sure about your 10C capacity I've always been told to fast charge Nicads and NiMh batteries at no more then 2C I believe the charger inculded with your radio charges the batteries at 1/10C or about 50/60Mah