Do (double) duty as American verb phrase
Used to describe a person who does more than one task, duty, role or job simultaneously
She is making use of her own abilities to make a living, so she is doing double duty as a full-time banker and a part-time tutor.
Used to describe something that is capable of serving two functions
I really like this piece of furniture as it does double duty as a desk and a bookshelf.
To become someone's work.
The verb "do" should be conjugated according to its tense.
Daughter: So I really want all my friends to have a great time. I was thinking it would be a good idea to have some candy out on the tables for people to snack on.
Mother: Well, if you want them to really enjoy themselves, candy is dandy but liquor is quicker.