$\dfrac{11}{5} - \dfrac{11}{15} = \dfrac{33}{15} - \dfrac{11}{15} = \dfrac{22}{15} $
$ \dfrac{5}{3} - \dfrac{4}{5} = \dfrac{25}{15} - \dfrac{12}{15} = \dfrac{13}{15} $
$\dfrac{6}{7} - \dfrac{6}{5} = \dfrac{30}{35} - \dfrac{42}{35} = \dfrac{-12}{35} $