42 7 3 / 60 12 21 =

\( \frac{42}{60} : \frac{7}{12} : \frac{3}{21} = \frac{42}{60} \times \frac{12}{7} \times \frac{21}{3} = \frac{42 \times 12 \times 21}{60 \times 7 \times 3} = \frac{10584}{1260} = \frac{84}{10} = \frac{42}{5} \)

Ответ: \( \frac{42}{5} \)