Answer:
10 km
Explanation:
For this problem, set up a ratio- you know that 6cm = 15km, and need how many km are represented by 4cm. Cross multiply so that you get 6/15 = 4/x, then 60 = 6x, and x (the value you are trying to solve for ) is equal to 10, or 10 km.
Hopefully this helps- let me know if you have any other questions!