The rate of taxation or interest is the amount of tax or interest that needs to be paid. It is expressed as a percentage of the amount that is earned, gained as profit, or borrowed.

我先把英语翻译出来：

【翻译】税率或利率是需要支付的税额或利息。它表示为收入、利润或借款金额的百分比。

看不同颜色的单词相对应：

The rate of taxation or interest：一个 rate 后面管着两个名词的“率”，也就是说：taxation or interest 共用一个 rate。

the rate 是单数，所以，It 指代The rate of taxation or interest。

the amount of tax or interest：the amount 后面也是两个名词，指“税额和利息”。

一个是“率”，一个是“额”。