let's firstly convert the mixed fractio to improper fraction.
[tex]\stackrel{mixed}{3\frac{1}{6}}\implies \cfrac{3\cdot 6+1}{6}\implies \stackrel{improper}{\cfrac{19}{6}} \\\\[-0.35em] ~\dotfill[/tex]
[tex]\begin{array}{ccll} Km s&Hour\\ \cline{1-2} \frac{19}{6}&\frac{1}{4}\\[1em] x&1 \end{array}\implies \cfrac{~~ \frac{19}{6}~~}{x}~~ = ~~\cfrac{~~ \frac{1}{4}~~}{1}\implies \cfrac{~~ \frac{19}{6}~~}{\frac{x}{1}}=\cfrac{1}{4}\implies \cfrac{19}{6}\cdot \cfrac{1}{x}=\cfrac{1}{4} \\\\\\ \cfrac{19}{6x}=\cfrac{1}{4}\implies 76=6x\implies \cfrac{76}{6}=x\implies \cfrac{38}{3}=x\implies 12\frac{2}{3}=x[/tex]
