5 cm = 2 km?. I don't think so. Are you asking how many cm are in 5.6 km?.
What's nice about the metric system is that it's all based on multiples of 10.
There are 100 cm in 1 m and there are 1000 m in 1 km, so how many cm are in 5.6 km?.
EDIT: I am sorry, I see what you mean. It's a scale like what may be on blueprints.
In that event, divide 2 into 5.6 and then multiply by 5.