계세요: 계십니다 or 계시답니다 are all formal forms..but the latter two are more formal than the previous one,and the last one"kye si tap ni ta"is used especially when you meet your boss,people who are older than you ,as well as strangers Hope my answer is useful Semoga sukses!! xD

the formal form is "계십니다" but if u wanna ask someone older, don't forget to change "~입니다/ㅂ니다" to "입니까/ㅂ니까?" ;) hope my answer will help u ^^