We are given that on a map the distance of 5 miles is equivalent to 5/6 cm, we are asked to determine the actual distance if the map shows 3 1/2 cm. To do that, we need to find the proportion between actual distance and ditance on the map, we do that by dividing the known actual and map distances, like this:
![k=(5miles)/((5)/(6)cm)=6\frac{miles}{\operatorname{cm}}]()
Now, we multiply the distance on the map for which we want to find its actual equivalence since this proportion must be constant for any distance on the map. We get:
![6\frac{miles}{\operatorname{cm}}*(3(1)/(2)cm)=(6)((7)/(2))miles=21\text{ miles}]()
Therefore, the actual distance is 21 miles