Step-by-step explanation:
9.
[tex] \frac{8}{9} + \frac{5}{9} = \frac{8 + 5}{9} = \frac{13}{9} [/tex]
10.
[tex] \frac{6}{12} + ( - \frac{14}{12} ) = \frac{6 - 14}{12} [/tex]
11.
[tex] \frac{ - 6 + 3}{8} = \frac{ - 3}{8} [/tex]
12.
[tex] \frac{9 - 7}{20} = \frac{2}{20} = \frac{1}{10} [/tex]
