Adding Guests & Multiply Price

I need to add the ability for customers to choose from a drop down menu 1-10 for number of guests when booking an appointment and choosing a day and time. It also needs to multiply the time slot by the number of guests. So if the service was 1 hr for each guests choosing 5 guests would lock the next 5 hours on the calendar. It would simply then multiply the price by the number of guests. I'm using the appointments+ plugin out of the box with no mods. Please help other members badly need this options to be competitive with other software.