SOLUTION
From the question, you currently make 15% flat commission on all sales.
Since you make an average of $3,980 in sales weekly, then Gross income becomes
[tex]\begin{gathered} 15\%\text{ of }$3,980$ \\ =\frac{15}{100}\times$3,980$ \\ =\frac{59,700}{100} \\ =597\text{ dollars } \end{gathered}[/tex]Hence the answer is $597 weekly