[tex]\bf \cfrac{9}{10}-x=\cfrac{1}{2}\implies \stackrel{\textit{multiplying both sides by }\stackrel{LCD}{10}}{10\left( \cfrac{9}{10} -x \right)=10\left( \cfrac{1}{2}\right)}\implies 9-10x=5 \\\\\\ 9=5+10x\implies 4=10x\implies \cfrac{\stackrel{2}{~~\begin{matrix} 4 \\[-0.7em]\cline{1-1}\\[-5pt]\end{matrix}~~}}{\underset{5}{~~\begin{matrix} 10 \\[-0.7em]\cline{1-1}\\[-5pt]\end{matrix}~~}}=x\implies \cfrac{2}{5}=x[/tex]
