[tex]\bf \begin{array}{ccll} wall&paint\\ \cline{1-2}\\ \frac{3}{4}&\frac{1}{7}\\\\ x&1 \end{array}\implies \cfrac{~~\frac{3}{4}~~}{x}=\cfrac{~~\frac{1}{7}~~}{1}\implies \cfrac{~~\frac{3}{4}~~}{\frac{x}{1}}=\cfrac{1}{7}\implies \cfrac{3}{4}\cdot \cfrac{1}{x}=\cfrac{1}{7} \\\\\\ \cfrac{3}{4x}=\cfrac{1}{7}\implies 21=4x\implies \cfrac{21}{4}=x\implies 5\frac{1}{4}=x[/tex]
