let's firstly convert the mixed fraction to improper fraction.
[tex]\bf \stackrel{mixed}{7\frac{1}{2}}\implies \cfrac{7\cdot 2+1}{2}\implies \stackrel{improper}{\cfrac{15}{2}} \\\\\\ \begin{array}{ccll} pies&\stackrel{flour}{cups}\\ \cline{1-2}\\ 6&\frac{15}{2}\\ 9&x \end{array}\implies \cfrac{6}{9}=\cfrac{~~\frac{15}{2}~~}{x}\implies \cfrac{2}{3}=\cfrac{~~\frac{15}{2}~~}{\frac{x}{1}}\implies \cfrac{2}{3}=\cfrac{15}{2}\cdot \cfrac{1}{x} \\\\\\ \cfrac{2}{3}=\cfrac{15}{2x}\implies 4x=45\implies \cfrac{4}{45}=x[/tex]
