$128,000 represents 100%
To find how much is 4% we can use the next proportion:
[tex]\frac{128,000\text{ \$}}{x\text{ \$}}=\frac{100\text{ \%}}{4\text{ \%}}[/tex]Solving for x:
[tex]\begin{gathered} 128,000\cdot4=100\cdot x \\ \frac{512,000}{100}=x \\ 5,120=x \end{gathered}[/tex]Her commission is $5,120
