SOLUTION
Step1: Define the parameters
[tex]\begin{gathered} x=sales \\ y=\text{weekly salary} \end{gathered}[/tex]Step2; Write out a linear expression
[tex]\begin{gathered} \text{ 3\% of his sales=}\frac{\text{3}}{100}\times x=0.03x \\ \text{then } \\ y=0.03x+500 \end{gathered}[/tex]To make $800 in a week, then y = $800
Step3: Substitute the value of y into the expression
[tex]\begin{gathered} y=0.03x+500 \\ 800=0.03x+500 \\ 800-500=0.03x \\ 300=0.03x \end{gathered}[/tex]Then the value of x is
[tex]\begin{gathered} x=\frac{300}{0.03}=10000 \\ x=10000 \end{gathered}[/tex]Therefore, he must make 10000 sales to earn at least $800 in a week
