Think of this question as being like a die that you would use to play monopoly with. A die has 6 sides right? Or a sugar cube. That has six sides. So a rectangular prism has the same number of sides.
I just thought of something. Do you mean faces or edges? There are 12 edges and 6 faces or sides. I hope that's what you mean.
6 faces <<<< answer
12 edges where 2 faces meet <<<< answer