7)7-4;

$$7 \frac{10}{21} - 4 \frac{16}{21} = 6 \frac{31}{21} - 4 \frac{16}{21} = (6 - 4) + (\frac{31}{21} - \frac{16}{21}) = 2 + \frac{15}{21} = 2 + \frac{5}{7} = 2 \frac{5}{7}$$

Ответ: $$2 \frac{5}{7}$$