[tex]\begin{array}{ccll} \stackrel{cups}{sugar}&cookies\\ \cline{1-2} \frac{3}{4}&24\\[1em] x&18 \end{array}\implies \cfrac{ ~~ \frac{3}{4} ~~ }{x}~~ = ~~\cfrac{24}{18}\implies \cfrac{ ~~ \frac{3}{4} ~~ }{\frac{x}{1}}~~ = ~~\cfrac{4}{3}\implies \cfrac{3}{4}\cdot \cfrac{1}{x}=\cfrac{4}{3} \\\\\\ \cfrac{3}{4x}=\cfrac{4}{3}\implies 9=16x\implies \cfrac{9}{16}=x[/tex]
now, the fraction is not an improper one, thus we can't quite put it in a mixed format, unless you count 0 as its whole, then I guess we can say is [tex]0\frac{9}{16}=x[/tex]