Dynamic Dropdown List on Form

DPS Finance

I'm working on creating a form for travel document submission. They have to submit travel documents by specific trip number. I want to make the drop down list for trip numbers dependent on the division the select. ie They select Division A, they only get a list of trip numbers for Division A.

Additionally I want to limit the trip numbers from being used more than once. I'm guessing that would be a dynamic dropdown as well.