\(\begin{array}{l}x:\frac{3}{4} = \frac{5}{8}:\frac{3}{4}\\x:\frac{3}{4} = \frac{5}{8} \times \frac{4}{3} = \frac{5}{6}\\x = \frac{5}{6} \times \frac{3}{4}\\x = \frac{5}{8}\end{array}\)
\(\begin{array}{l}\frac{1}{5} \times x = \frac{2}{3} - \frac{4}{6}\\\frac{1}{5} \times x = 0\\\,\,\,\,\,\,\,\,x = 0\end{array}\)