[tex]\bf \cfrac{x}{5}-\cfrac{x}{7}=3\impliedby
\begin{array}{llll}
\textit{let's multiply both sides by }\stackrel{LCD}{35}\\
\textit{to do away with the denominators}
\end{array}
\\\\\\
35\left( \cfrac{x}{5}-\cfrac{x}{7}\right)=35(3)\implies 7x-5x=105
\\\\\\
2x=105\implies x=\cfrac{105}{2}[/tex]
