How do you simplify 2/7 - 2/21?

$\frac{2}{7} - \frac{2}{21} = \frac{4}{21}$
$\frac{2}{7} - \frac{2}{21} = \frac{2}{7} \cdot \frac{3}{3} - \frac{2}{21} = \frac{6}{21} - \frac{2}{21} = \frac{4}{21}$