usedto后加什么？

　　This formula is used to calculate the area of a circle.

　　这个公式用于计算圆的面积。

　　It's very different to what I'm used to.

　　这与我所习惯的大不相同。

　　We're used to the noise from the traffic now.

　　现在我们已经适应车辆往来的噪音了。

　　All I know is that she used to work in a bank.

　　我只知道她曾在银行工作过。