To solve the exercise you can use a rule of three, like this:
[tex]\begin{gathered} \text{\$}15,725\rightarrow100\text{\%} \\ \text{\$}x\rightarrow4.25\text{\%} \\ x=\frac{4.25\text{\%}\cdot\text{ \$15,725}}{100\text{\%}} \\ x=\text{ \$}\frac{4.25\cdot\text{15,725}}{100} \\ x=\text{ \$}\frac{68831.25}{100} \\ x=\text{ \$668.31} \end{gathered}[/tex]Therefore, the commission earned will be $668.31.
