Calculate Commissions

Hi

I am very new to databases, and think i am a bit over my head. I am doing a database for vacation rentals, and am trying to calculate commissions, basically i wanted to have a set of checkboxes, labeled 10%, 15%, 2.5% and $25, with any combination of these checkboxes being able to be checked.

i want the query to work like this:

If the 10% checkbox is checked i want the query to take the SubTotal for the reservation, and calculate 10% of that number. if the 2.5% checkbox is also checked, i want the query to calculate 2,5% of the reservation and add it to the commissions total (10% + 15%)

I think(hope) that i explained that clearly? Can this be done?

Thanks for your help!

Ben