5)5-3+4

$$5\frac{17}{21} - 3\frac{8}{21} + 4\frac{7}{21} = (5 - 3 + 4) + (\frac{17}{21} - \frac{8}{21} + \frac{7}{21}) = 6 + \frac{17 - 8 + 7}{21} = 6 + \frac{16}{21} = 6 \frac{16}{21}$$

Ответ: $$6 \frac{16}{21}$$