The rule for division by a fraction is "change to multiplication by the reciprocal."
So you want(4/3)(12) which is 4(4) = 16
[tex]\bf 12\div \cfrac{3}{4}\implies \cfrac{12}{1}\div\cfrac{3}{4}\implies \cfrac{\stackrel{4}{~~\begin{matrix} 12 \\[-0.7em]\cline{1-1}\\[-5pt]\end{matrix}~~}}{1}\cdot \cfrac{4}{~~\begin{matrix} 3 \\[-0.7em]\cline{1-1}\\[-5pt]\end{matrix}~~}\implies 16[/tex]
