Dropdown data depends on filters in another field.

Dropdown data depends on filters in another field.

In my quote form I have a lookup field called Reseller that pulls from Accounts.  I would like it to pull from Accounts, but only those accounts with an account field 'Type' where that is 'Reseller'.  Does anyone know a way to do this?

Similarly, I'd like to have another field called 'Reseller Rep' that only pulls 'Contacts' from that Account-type-Reseller previously selected.