GraceFam2016

Hi, I have a form that has several fields that need to be calculated and show the user, the final total in the Amount Due field. Example. The user will choose the number of adults attending, if the person types in 2, the 2 should be multiplied by $50.00 which will show $100.00 to the user in the Amount Due field. Is this possible to do with a submit form?

I have a form that I have attached to my webpage, however, I need to make changes to the form so that it will calculate when the attendees to the family reunion submit the number of persons attending the reunion. Where do I add the calculation so that it will show the Amount Due in the Amount Due field?