Formula - List - extracting characters

I am straggling with Formula

I have two lists: one list of parameters with only room type references and second set of parameters type reference and “_” description.

I am looking for Formula and a way to :

  1. get all first 3 characters from name

  2. get all character till “_”

so I know who to deal with those two methods in case of more complex text

F71, F35, F75, F71,

F71_WC, F35_Office, F75_Car_Park, F35_Office

so I would like to see:

True, True, True, False