Kalau gak salah rumusnya ialah
rumus question tag S+aux verb (tobe, tohave, to do,and modals ) + obj, + auxverb(ditambah not atau tidaknya tergantung dari aux verb yg dipakai sebelumnya +S

example : she is a teacher, isn't she ?
he isn't a doctor, is he ?
they will do it, won't they?
i study english, don't i ?
i have opened the door, haven't i?
she hasn't closed the door, has she?