[tex]\bf \begin{array}{ccll} cookies&\stackrel{butter}{cups}\\ \cline{1-2} 20&\frac{1}{3}\\\\ 12&x \end{array}\implies \cfrac{20}{12}=\cfrac{~~\frac{1}{3}~~}{x}\implies \cfrac{5}{3}=\cfrac{~~\frac{1}{3}~~}{\frac{x}{1}}\implies \cfrac{5}{3}=\cfrac{1}{3}\cdot \cfrac{1}{x} \\\\\\ \cfrac{5}{3}=\cfrac{1}{3x}\implies 15x=3\implies x = \cfrac{3}{15}\implies x = \cfrac{1}{5}[/tex]
