How much should i charge for babysitting?

I'm 16 & have a 3 year old named Samantha& I'm also 8 weeks pregnant. Well my aunt is working all summer & so is her husband and she needs a babysitter...and i need extra money. So I told her I would watch her daughter Cami (5 years old)...she told me she would love that and asked how much i want to get paid. I told her i'll tell her tommorow and she said ok. So how much should i charge per hour?