Verified Answer :

\(\dfrac{6}{18} = \dfrac{x}{36}\) 

\(\dfrac{1}{3} = \dfrac{x}{36}\) 

\(\dfrac{1}{3} * 36 = x\)   \(|Multiply \ by \ 36|\)

\(x= \dfrac{36}{3}\)  \(|Divide \ both \ sides \ by \ 3|\)

\(x=12\)