29. \(\frac{1}{\frac{1}{42}+\frac{1}{91}}\)

\(\frac{1}{42}+\frac{1}{91}=\frac{13}{546}+\frac{6}{546}=\frac{19}{546}\).

\(1:\frac{19}{546}=\frac{546}{19}\).

Ответ: \(\frac{546}{19}\).