\(a,\dfrac{x}{4}=\dfrac{35}{28}\)
\(\Leftrightarrow28x=35.4\)
\(\Leftrightarrow28x=140\)
\(\Leftrightarrow x=5\)
\(b,5\dfrac{4}{7}:x=13\)
\(\Leftrightarrow\dfrac{39}{7}:x=13\)
\(\Leftrightarrow x=\dfrac{39}{7}:13\)
\(\Leftrightarrow x=\dfrac{3}{7}\)
\(f,\dfrac{2}{5}-\dfrac{1}{5}:x=-25\%\)
\(\Leftrightarrow\dfrac{1}{5}:x=\dfrac{2}{5}+\dfrac{1}{4}\)
\(\Leftrightarrow\dfrac{1}{5}:x=\dfrac{13}{20}\)
\(\Leftrightarrow x=\dfrac{1}{5}:\dfrac{13}{20}\)
\(\Leftrightarrow x=\dfrac{4}{13}\)
\(j,\left(2\dfrac{4}{5}x-50\right):\dfrac{2}{3}=51\)
\(\Leftrightarrow\dfrac{14}{5}x-50=51.\dfrac{2}{3}\)
\(\Leftrightarrow\dfrac{14}{5}x=34+50\)
\(\Leftrightarrow x=84:\dfrac{14}{5}\)
\(\Leftrightarrow x=30\)
