What to charge for family portraits?

I am not a professional, obviously because i am asking this question on yahoo answers haha. but i was asked to do family portraits and how much do i charge. i have no idea what to charge. i only have a simple dslr and a kit lens which is 18 - 55mm and a dinky tripod. but obviously they saw my pictures i have taken and they like the quality. but thos pictures are mainly of still life. only a handful of those are of people. please help
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family portraits