Editable pdf: calculated fields

I am trying to make a registration form in an edible PDF. I simply want to have one box calculate a total. For example the ticket price for this event is $35. I want the number of attendees selected, whether it be one or two automatically generate the price. so if 2 people are coming to this event their total ticket price would be $70. I have tried all calculations to enter in the calculate tab and cannot get the correct one. How can I get my form to generate a ticket price of $35 based on the number of attendees. What exact text would I enter, and where I put it it to get it to generate?! Help please