Returning a $ value if a checkbox return true

Hello All,

I am trying to set up an Excel formula that calculates a $ value if a checkbox returns true or false.

Basically, if the checkbox is checked, the COST amount needs to be multiplied by the QTY value. I've attached a screen shot of the basic table.

Right now I have a basic SUM working using: =SUM(COST*QTY) but I need to include a checkbox if statement I believe. I've tried everything but can't get it to work.

Can anyone help? I'm sure it's very simple.