\(\left(8\dfrac{4}{5}x-50\right):40\%=51\)
\(\left(\dfrac{44}{5}x-50\right):\dfrac{2}{5}=51\)
\(\dfrac{44}{5}x-50=51\cdot\dfrac{2}{5}\)
\(\dfrac{44}{5}x-50=\dfrac{102}{5}\)
\(\dfrac{44}{5}x=\dfrac{102}{5}+50\)
\(\dfrac{44}{5}x=\dfrac{352}{5}\)
\(x=\dfrac{352}{5}:\dfrac{44}{5}\)
\(x=8\)
Vậy \(x=8\).