$\dfrac{-2}{7}+\dfrac{1}{5}:\dfrac{7}{15}$
$=\dfrac{-2}{7}+\dfrac{1}{5}\cdot\dfrac{15}{7}$
$=\dfrac{-2}{7}+\dfrac{3}{7}$
$=\dfrac{1}{7}$
$\dfrac{6}{7}+\dfrac{5}{7}:5-\dfrac{8}{9}$
$=\dfrac{6}{7}+\dfrac{5}{7}\cdot\dfrac{1}{5}-\dfrac{8}{9}$
$=\dfrac{6}{7}+\dfrac{1}{7}-\dfrac{8}{9}$
$=\dfrac{7}{7}-\dfrac{8}{9}$
$=1-\dfrac{8}{9}$
$=\dfrac{1}{9}$
$\dfrac{1}{4}+\dfrac{3}{4}(\dfrac{-1}{2}+\dfrac{2}{3})$
$=\dfrac{1}{4}+\dfrac{3}{4}\cdot\dfrac{1}{6}$
$=\dfrac{1}{4}+\dfrac{1}{8}$
$=\dfrac{3}{8}$
