Answer:
I believe that this expression would be classified as hyperbole.
Explanation:
It is a hyperbole because it's a stretch from the truth, they (being "we") didn't actually walk a hundred miles.
If you can change the wording and have it still make sense, you've found the answer.
SHE is the newest candidate for city council.
HER is the newest candidate for city council.
HERS is the newest candidate for city council.
The answer is A because it's the only one that makes sense.