你还没找零钱给我呢。

Nǐ hái méi zhǎo língqián gěi wǒ ne.

You still haven't returned my change.

这些零钱可以用来买地铁票。

Zhèxiē língqián kěyǐ yònglái mǎi dìtiěpiào.

This change can be used to buy a subway ticket.

你可以帮我换些零钱吗？

Nǐ kěyǐ bāng wǒ huàn xiē língqián ma?

Can you help me make small change?