I have a form that includes a state field. 
It also has a region field. 
Depending on what has been selected in the state value/field,  I want the region field to populate with one of these 5 regions:
West
Midwest
Southwest
Southeast
Northeast
 
So, if someone selects California in the state field of the form, the region field would automatically be selected as West.
What is the best way to accomplish this?
 
I'm new to the embedding/nesting forms -- as well as everything formidable.
 
Thanks!