1.

[tex]8 \frac{3}{7} + ( - 4 \frac{2}{3} ) - ( - 5 \frac{10}{21} ) = 8 \frac{9}{21} - 4 \frac{14}{21} + 5 \frac{10}{21} = 13 \frac{19}{21} - 4 \frac{14}{21} = 9 \frac{5}{21} [/tex]

2.

[tex]3 \frac{5}{6} + ( - 5 \frac{5}{8} ) - ( - 3 \frac{5}{12} ) - 2 \frac{2}{3} = 3 \frac{20}{24} - 5 \frac{15}{24} + 3 \frac{10}{24} - 2 \frac{16}{24} = \\ = 6 \frac{30}{24} - 7 \frac{31}{24} = - 1 \frac{1}{24} [/tex]