a)\(\frac{x}{21}=\frac{1}{2}\Rightarrow2x=21\Rightarrow x=\frac{21}{2}\)
b)\(\frac{2}{x}=\frac{3}{14}\Rightarrow28=3x\Rightarrow x=\frac{28}{3}\)
c)\(\frac{13}{9}=\frac{x}{18}\Rightarrow9x=234\Rightarrow x=\frac{234}{9}=26\)
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