ㅂ니다 그러다

"…," they said — quoting formal speech

A sentence in the formal polite -ㅂ니다/-습니다 style, then 그러다 "says, goes", reporting the words as spoken: "it's 30,000 won for six months," he goes; "our boss is a fan," she said, striking up a conversation; "I'm really sorry," he said. The quoted part keeps its politeness while 그러다 stays casual, so the speaker is narrating informally about something said formally. Watch out: 그러면 or 그러려고 after -ㅂ니다 can instead just mean "then" or "for that", which is what several lines here do, including the one about the second quiz question.

Register: casual narration of formal speech