a.
[tex] \frac{2}{7} + \frac{10}{21} = \frac{6}{21} + \frac{10}{21} = \frac{16}{21} [/tex]
b.
[tex]1 - \frac{16}{21} = \frac{21}{21} - \frac{16}{21} = \frac{5}{21} [/tex]
