How much should we pay our babysitter?

My husband and I are new parents. We do not know how much to pay our babysitter. Our baby is 2 months old. The sitter is 16. The sitter comes to the house one day for 8 hours, and another for 4 hours (so a total of 12 hours a week). All she has to do is change diapers as needed, and do a couple of feedings. The rest of the time she either just snuggles the baby, or reads to the baby. If the baby is calm or sleeping the sitter is free to watch tv, eat our food, etc. We don't know how much we should pay her. Help!