How much to pay babysitter?

So Im going back to work and my neighbors teenage daughter said she would babysit. I'll be needing her from 2:30-4pm Mon-Fri. I have 3 kids who will be turning 5 and 2 very soon. How much would you pay a babysitter every week? (I wanted to ask on here to get back to her with a fair weekly pay)

She's not expected to do anything other then watching the kids. They will be locked up in the living room area and she would just have to sit and watch them and just change diapers as needed.