-18: (4-(-6)+21); 6) -3.4 + 2 \frac{1}{5} : \left(-\frac{22}{35}\right); B) -2.13 - (-5).

Решение:

• Пример 1:
  \( -18 : (4 - (-6) + 21) = -18 : (4 + 6 + 21) = -18 : 31 = -\frac{18}{31} \)
• Пример 6:
  \( -3.4 + 2 \frac{1}{5} : \left(-\frac{22}{35}\right) = -3.4 + \frac{11}{5} : \left(-\frac{22}{35}\right) = -3.4 + \frac{11}{5} \times \left(-\frac{35}{22}\right) = -3.4 - \frac{11 \times 35}{5 \times 22} = -3.4 - \frac{1 \times 7}{1 \times 2} = -3.4 - 3.5 = -6.9 \)
• Пример B:
  \( -2.13 - (-5) = -2.13 + 5 = 2.87 \)

Ответ:

• -18 : (4-(-6)+21) = -18/31
• -3.4 + 2 1/5 : (-22/35) = -6.9
• -2.13 - (-5) = 2.87