Задача 7. \(\frac{7^4\cdot3^4}{21^2}\)

\[\frac{7^4\cdot 3^4}{21^2}=\frac{(7\cdot3)^4}{21^2}=\frac{21^4}{21^2}=21^{4-2}=21^2=441.\]

Ответ: 441.