Applying Math to getting rides

Here is an attempt, to apply math to the real real world and what the limits are.

I do not drive so I sometimes need a ride home (about once every two weeks). SO, who to ask? If giving me a ride home adds alot of time to their normal ride, then I would ask them less often. How to quanify this?

If person x has to go i minutes out of his way, then I will ask person x at most once every i weeks.

But here are problems with the formula:

1. Let say that person x normally takes 5 minutes to get home, but giving me a ride home will add 10 minutes, yielding a 15 minute ride. Let say that person y normally takes 30 minutes to get home, but giving me a ride home will add 10 minutes, yielding a 40 minute ride. Person x may view giving me a ride as tripling the time home, while Person y views it as adding just 10 minutes. On the other hand, Person y already has a 30 minute ride and may not want to add anything to it.
2. How much do they like my company? Is i minutes with Bill seem like log i minutes, &radic i , i/2, i, 2i, or i², minutes (past i² and I won't ever ask for a ride). (OFF TOPIC QUESTION- how do you do a good sqrt symbol in html? Whats above is the best I could find.)
3. Ditto for how much I like their company.
4. What if when giving me a ride home they pass by their own house and have to backtrack? Even if its not too many extra minutes it has a psycological effect.
5. How complicated is x's life? If x has to drop one of their kids at soccer practice, and one at Piano lessons then fitting a ride for me into it may be complicated even if it is not that many minutes out of the way.
6. Giving someone a ride TOO school is far worse then giving someone a ride FROM school, since FROM school both parties can be more flexible.