Let's shake on it:

一言為定

例句：

It seems that we have a deal, so let's shake hands on it. 

看來(lái)我們成交了，一言為定吧。

It's a deal:

一言為定

例句：  

You can use my car this weekend. It's a deal.

你周末可以用我的車(chē)。一言為定。

We got a deal:

一言為定

例句：     

If you clean the house, I'll take the kids to the swimming lesson.

如果你打掃房子，我就帶孩子去上游泳課。

OK, it's a deal.

OK，一言為定。

Song for you（片尾曲）

Alan Walker、Iselin Solheim - Faded