Translate the Given Formula to an English Phrase Using the Word

Short Answer

Translate the given formula to an English phrase using the word "varies".
- $\mathrm { I } = \mathrm { PRT }$ , where $\mathrm { I }$ is the simple interest on a principal of $\mathrm { P }$ dollars invested for $\mathrm { T }$ years at an interest rate of $\mathrm { R }$ per year