8. \(8\frac{5}{21}+4\frac{19}{21}=\)

\(8+4=12\), а \(\frac{5+19}{21}=\frac{24}{21}=1\frac{1}{7}\).

\(12+1\frac{1}{7}=13\frac{1}{7}\).

Ответ: \(13\frac{1}{7}\).