quantity box?

Hi all, I'm using on Appointments+ on this page.

Is there a way to add a "quantity" box? For example, this business will be renting out jet ski's, and I assume most people will be wanting to rent 1, 2, 3 or 4 at a time... I don't want to make customers fill out the form 4 different times to reserve 4 jet ski's for their family. At the same time, adding various services ("One Jet Ski - 1 Hour", "Two Jet Ski's - 1 hour", etc, etc - like it's setup now) is clogging up the dropdown menu and not very user friendly... any ideas? Thanks