her earnings were "x", which incidentally enough is 100%, now, we also know that "x" went up by 6%, which is $3120, thus
[tex]\bf \begin{array}{ccll}
amount&\%\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
x&100\\
3120&6
\end{array}\implies \cfrac{x}{3120}=\cfrac{100}{6}\implies x=\cfrac{3120\cdot 100}{6}[/tex]
