반말? 존댓말?

Hoya says 카드로 계산할게.

Sori says 카드로 계산할게요.

The staff are strangers, so the ending stays 해요체. 계산할게 (without 요) is casual speech for a friend — easy to slip into right after talking to Bori.

Learn it in Life in Korea · Unit 3

Hoya says ㅇㅇ 알겠어.

Sori says 네, 알겠어요.

Sori-ssaem is your teacher, so the ending stays 해요체 with 요. ㅇㅇ and 알겠어 are for a friend you speak casually with, even in a text.

Learn it in Life in Korea · Unit 4

Hoya says 계좌를 만들고 싶어.

Sori says 계좌를 만들고 싶은데요.

The clerk is a stranger: use 해요체. 싶어 is 반말, for Bori; at a counter say 싶은데요 (or 싶어요).

Learn it in Life in Korea · Unit 7

Hoya says 일요일에 놀러 갈게.

Sori says 일요일에 놀러 갈게요.

She speaks 반말 to you because she is older. You are younger and she is your friend's parent, so you answer in 해요체 — and you keep it. 반말 (갈게) is for Bori.

Learn it in Life in Korea · Unit 8

Hoya says 빨래방 오른쪽이야.

Sori says 빨래방 오른쪽이에요.

You kept the ending you had just used with Bori. The ending follows the person you are speaking to now: Bori gets 반말, the rider gets 해요체.

Learn it in Life in Korea · Unit 5

Hoya says 안녕히 가세요.

Sori says 안녕히 계세요.

You say 가세요 ('go well') to someone who is leaving, and 계세요 ('stay well') to someone who is staying. You are leaving and the clerk stays, so you say 안녕히 계세요.

Learn it in Life in Korea · Unit 2