Answer:
d = 20.6 miles
Explanation:
Given that,
Two sales representatives leave from the same office. One travels 20 miles due north and the other travels 5 miles due west.
It is required to find the distance between two representatives. It it is d. It can be calculated as the resultant if two values as follows :

So, the sales representative are 20.6 miles apart. Hence, the correct option is (c).