We are given the following information.
The monthly salary of a showroom attendant is the sum of a fixed salary of $600 plus 8% of all monthly sales.
We are asked to determine the monthly sales for which her monthly salary reaches $1,800.
Let y be the monthly salary and x be the monthly sales.
Then we can set up the following equation
[tex]y=600+0.08x[/tex]Where 600 is the fixed salary and 0.08x is 8% of all monthly sales.
Substitute y = $1,800 into the equation and solve for x.
[tex]\begin{gathered} 1800=600+0.08x \\ 1800-600=0.08x \\ 1200=0.08x \\ \frac{1200}{0.08}=x \\ 15,000=x \\ x=\$15,000 \end{gathered}[/tex]Therefore, the monthly sales are $15,000.