Answer:
15 miles.
Step-by-step explanation:
5 + 10 = 15
5 represents the fact that he walked 5 miles east, and then if he were to walk from there towards the west, that would be 10 miles because if its 5 miles from his starting point to the east, then it would be double from the east to the west so if you add 5 miles and 10 miles, you should get a total of 15 miles.
I hope this helps you :D