$\frac{12}{36}=\frac{1}{3}$

$\frac{12}{36}=\frac{6}{18}$

$\frac{16}{72}=\frac{2}{9}$

$\frac{16}{72}=\frac{8}{36}$

$\frac{28}{42}=\frac{14}{21}$

$\frac{28}{42}=\frac{4}{6}$