\(a,\frac{2}{3}=\frac{x}{54}\Rightarrow x=\frac{2\times54}{3}\Rightarrow x=36\)
\(b,\frac{10}{x}=\frac{15}{6}\Rightarrow x=\frac{10\times6}{15}\Rightarrow x=4\)
\(c,\frac{2}{3}< \frac{x}{6}< 1\Rightarrow\frac{2}{3}\times6< x< 1\times6\Rightarrow4< x< 6\)