**Решение:**
**B.2:**
\[-\frac{2}{7} + \left(-3\frac{5}{7}\right) = -\frac{2}{7} - \frac{26}{7} = -\frac{28}{7} = -4\]
**B.3:**
\[-\frac{1}{4} + \left(-5\frac{3}{4}\right) = -\frac{1}{4} - \frac{23}{4} = -\frac{24}{4} = -6\]
**Ответ:** B.2: -4, B.3: -6