Question

if the mine winch drum diameter is 6cm,calculate hiw far far cage will drop for each single rotation of the drum, use the formula C=2nr

Answer 1

You have the formula, so use it.

If you don't know why to use the formula, you just don't understand the problem.
One turn of the wheel uses up enough rope to wrap around the circumference of the drum.
The formula gives you that circumference.