Who is going to participate in the walkathon?

W: Hey, Joe, what’s all this talk about the benefit walkathon this weekend?
M:Don’t you know, most of the residents in Packer Hall are going to try to walk the seven miles from the engineering library, across campus and down to city hall, in an effort to raise money for the new children’s hospital.
W: Sounds like a good idea. But I don’t understand where the money comes from?
M:Well, a few days before the walkathon, each participant goes around asking people to pledge just a certain amount of money each mile that he or she expects to walk in the e-vent. Then after the walkathon’s over, the participants go back to the same people, collect the money pledged and send into the hospital.
W: So you mean if someone pledges, say, a dollar a mile, and you walk five miles, you get five dollars?
M:That’s right of course, most of my friends aren’t such big spenders, the biggest pledge I’ve gotten so far is 25 cents a mile.
W: And how many people have made pledges for you?
M: Eleven so far, say, how about making it an even dozen?
W: Sure, if you do the same for me. The walkathon sounds like a perfect opportunity for me to break my new pair of sport shoes.