her totals sales were "x", now, if she sold "x", and made a 30% of "x" which is 1800, that simply means, "x" is the 100%
[tex]\bf \begin{array}{ccllll}
amount&\%\\
\textendash\textendash\textendash\textendash\textendash\textendash&\textendash\textendash\textendash\textendash\textendash\textendash\\
x&100\\
1800&30
\end{array}\implies \cfrac{x}{1800}=\cfrac{100}{30}[/tex]
solve for "x"
