Hello there!
I gotta say, that's right on my alley. I am used to wrapping my head around other people`s programming "exercises" improving or simply debugging them, in fact that's the niche I've chosen to make business in. I'd appreciate if you have some "to start with" list of issues to make a proper assessment of the job though. Just to spare any surprizes later on, as much a spossible.
And also there's one ting you should know. Even though the bid is for 20 hours of work, the calculated amount is what you pay no matter what the actual time expense end up being (more for example, regardless of whatever the reasons for the excess are) once we start actually working on the lot. That's the way I usually operate, because I think the risk should be shared between the parties, meaning that if I manage to finishe the whole lot in under 20 hours you still end up paying for 20, so if I don't manage to finish in 20 I think the "other" side of the risk should be on my behalf. That's just so you know there won't be any additional charging regarless of teh actual time spent to finish all aspects of the job.
Kind Regards,
Dobri