Answer:
B. 21 miles
Explanation:
The shortest overall route will be the sum of the shortest routes between way points.
The shortest route from the High School to the Airport is the direct route, 15 cm on the map. The shortest route from the Airport to Jill's house is via the High School and City Hall, a total of 15+12+21 = 48 cm on the map.
The shortest distance Jill can travel from work to home via the airport is ...
(15 cm +48 cm)/(3 cm/mi) = 21 miles