In this case, we'll have to carry out several steps to find the solution.
Step 01:
Data
Map distance = 3 cm
Scale
1 cm map = 2 km
Step 02:
1 cm map -------------- 2 km
3 cm map -------------- x
x * 1 cm map = 2 km * 3 cm map
x = (2 * 3) / 1 = 6 km
The actual distance will be: