Hey there! I'm happy to help!
We see that 4 cm represents 5 km. We want to see how much 5 cm represents.
To get from 4 cm to 5 cm, you multiply by 5/4. So, we multiply our 5 km by 5/4 to see how kilometers are represented by 5 centimeters on the mask.
5(5/4)=6 1/4
Therefore, the number of km represented by 5 cm on the map is 6 1/4 km.
Have a wonderful day! :D