Решение:

1. $$-4 + (-7) = -4 - 7 = -11$$
2. $$-0,46 + (-0,89) = -0,46 - 0,89 = -1,35$$
3. $$-2,3 + (-0,86) = -2,3 - 0,86 = -3,16$$
4. $$-5\frac{7}{9} + (-3\frac{4}{9}) = -5\frac{7}{9} - 3\frac{4}{9} = -8\frac{11}{9} = -9\frac{2}{9}$$
5. $$\frac{-5}{8} + (\frac{-11}{12}) = \frac{-5}{8} - \frac{11}{12} = \frac{-15}{24} - \frac{22}{24} = \frac{-37}{24} = -1\frac{13}{24}$$
6. $$-4\frac{5}{14} + (-7\frac{9}{21}) = -4\frac{5}{14} - 7\frac{3}{7} = -4\frac{5}{14} - 7\frac{6}{14} = -11\frac{11}{14}$$

Ответ:

1. $$\mathbf{-11}$$
2. $$\mathbf{-1,35}$$
3. $$\mathbf{-3,16}$$
4. $$\mathbf{-9\frac{2}{9}}$$
5. $$\mathbf{-1\frac{13}{24}}$$
6. $$\mathbf{-11\frac{11}{14}}$$