Help Writing a Script

Hi All -
I have a form that I need script form and I can't get it to work. I have a series of five check boxes with the responses ranging from 1 to 5 and want to add those responses together in another field when the user enters a response. For example, if the user enters the response of "5" for each check box, I want the total of each check box to show as "25" in another field. How do I write script for that?

Thanks.