If you travel 5 miles north then turn and travel 5 miles south, you have traveled miles. a0

15

Explanation:

If you have to go back from the northern position to the first position, you have to replace yourself a second time by 5 miles. Then you just need to add 5 again for the south.

i am pretty sure it is c because when people are closer together, they cannot move as freely. picture being in a mostly full elevator, for instance. the people are right next to you, and you can barely move.