Given:
[tex]\frac{x}{12}=\frac{3}{9}[/tex]
To solve for x, cross multiply to get
[tex]\begin{gathered} 9\times x\text{ = 3}\times12 \\ 9x\text{ = 36} \\ \text{Divide both sides by 9} \\ \frac{9x}{9}=\text{ }\frac{36}{9} \\ x\text{ = 4} \end{gathered}[/tex]
