\(\left[\left(6\dfrac{3}{5}-3\dfrac{3}{14}\right)\cdot2,5\right]:\left(21-1,25\right)=x:5\dfrac{5}{6}\\ \Leftrightarrow\dfrac{237}{70}\cdot\dfrac{5}{2}:\dfrac{79}{4}=x:\dfrac{35}{6}\\ \Leftrightarrow x:\dfrac{35}{6}=\dfrac{3}{7}\\ \Leftrightarrow x=\dfrac{3}{7}\cdot\dfrac{35}{6}=\dfrac{5}{2}\)
\(\left[\left(6\dfrac{3}{5}-3\dfrac{3}{14}\right)\cdot\dfrac{5}{2}\right]:\left(21-1.25\right)=x:5\dfrac{5}{6}\)
\(\Leftrightarrow x:\dfrac{35}{6}=\dfrac{3}{7}\)
hay \(x=\dfrac{5}{2}\)