a)
[tex] \frac{1}{9} + \frac{3}{9} = \frac{4}{9} [/tex]
[tex] \frac{4}{8} + \frac{2}{8} = \frac{6}{8} [/tex]
b)
[tex] \frac{10}{9} - \frac{6}{9} = \frac{4}{9} [/tex]
[tex] \frac{7}{4} - \frac{8}{8} = \frac{14}{8} - \frac{8}{8} = \frac{6}{8} [/tex]
