з) -3 3/14 - (-2 5/6).

з) -3\frac{3}{14} - (-2\frac{5}{6}) = -3\frac{3}{14} + 2\frac{5}{6} = -3\frac{9}{42} + 2\frac{35}{42} = -1 + \frac{26}{42} = -\frac{42}{42} + \frac{26}{42} = -\frac{16}{42} = -\frac{8}{21}. Приводим к общему знаменателю 42.