Ответ:

а) \(x=6\frac{2}{21}-3\frac{4}{7}=6\frac{2}{21}-3\frac{12}{21}=2\frac{11}{21}\). Проверка: \(2\frac{11}{21}+3\frac{12}{21}=6\frac{2}{21}\).

б) \(x=8\frac{5}{16}-5\frac{7}{12}=8\frac{15}{48}-5\frac{28}{48}=2\frac{35}{48}\). Проверка: \(5\frac{28}{48}+2\frac{35}{48}=8\frac{15}{48}=8\frac{5}{16}\).

Ответ: а) \(x=2\frac{11}{21}\); б) \(x=2\frac{35}{48}\).