Drop down list based on condition

Hi guys!
I need to make a drop down list depending on a value selected, here is what I have:

Basically I have a database for assets. I need to store the location of where the asset is, depending on the city it may have different factories, so the asset is in one of those factories.

So for example, the city of Miami has 3 factories, when I register a new asset I must pick the city and then the factory in where it's gonna be.

How would I do this with some drop down list?

thanks for the help