\(\dfrac{3}{x}+\dfrac{y}{3}=\dfrac{5}{6}\Leftrightarrow\dfrac{9}{3x}+\dfrac{xy}{3x}=\dfrac{5}{6}\)
\(\Leftrightarrow\dfrac{xy+9}{3x}=\dfrac{5}{6}\Leftrightarrow6\left(xy+9\right)=5\cdot3x\)
\(\Leftrightarrow6xy+54=15x\)\(\Leftrightarrow6xy-15x=-54\)
\(\Leftrightarrow3x\left(2y-5\right)=-54\)
\(\Leftrightarrow x\left(2y-5\right)=-18\)