Ответ:

  1. \(8\frac{3}{4}-x=3\frac{5}{16}\).

    \(x=8\frac{3}{4}-3\frac{5}{16}=8\frac{12}{16}-3\frac{5}{16}=5\frac{7}{16}\).

  2. \(x-9\frac{3}{7}+5\frac{8}{21}=6\frac{5}{14}\).

    Переносим слагаемые: \(x=6\frac{5}{14}-5\frac{8}{21}+9\frac{3}{7}\).

    \(x=\frac{18}{42}+9\frac{18}{42}=9\frac{36}{42}=9\frac{6}{7}\). Wait compute: first difference \(6 15/42-5 16/42=41/42\), then plus 9 18/42 = 9 +59/42=10 17/42.

    Следовательно, \(x=10\frac{17}{42}\).

Ответ: 1) x = 5 7/16; 2) x = 10 17/42.