請幫我翻譯朗文ADVANCED聽力 - 自學

p.253 Q.72
Man: Is it OK if I write a check for twenty dollars over the amount?
（我能開一張20元的支票付帳嗎？）

Woman: I can't cash checks at night. The cashiers only keep fifty
dollars' worth of change in the registers.
There's an ATM machine by the exit though.
（晚上我無法將支票兌現，出納員的收銀機裡只有五十塊的零錢，
出口處有台ATM）
Man: OK, I'll use that instead.

黃色部分的翻譯應該有問題
另外整題的邏輯我不懂：
check for twenty dollars 和 I can't cash checks at night.
The cashiers only keep fifty dollars' worth of change in the registers.
是什麼邏輯關係？

THX～

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