3-4 What's the fare?       

What's the fare?    How much do I owe you?   

How much should I pay?    Here you go.   Here is one hundred.   Just give me twenty back.   Keep the rest.    That's your tip.    Have a good one.

3-4 车费是多少钱？

我该给你多少钱？我该付多少钱？拿去吧。这里是一百元。只要找我二十元就好。其余的你留著。算是你的小费。再见。