Question

If the winch mine drum diameter is 6m, calculate how far the cage will drop for each single rotation of the drum, using the formula C =nr

Answer 1

You have the formula, though it is incorrect, so fix it and 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.

Answer 2

And it’s not ‘n’ — it’s π (pi)

Answer 3

and it is pi D not pi r