-2/7+1/5:7/15 6/7+5/7:5-8/9 1/4+3/4.(-1/2+2/3)

$\dfrac{-2}{7}+\dfrac{1}{5}:\dfrac{7}{15}$

$=\dfrac{-2}{7}+\dfrac{1}{5}\cdot\dfrac{15}{7}$

$=\dfrac{-2}{7}+\dfrac{3}{7}$

$=\dfrac{1}{7}$

$\dfrac{6}{7}+\dfrac{5}{7}:5-\dfrac{8}{9}$

$=\dfrac{6}{7}+\dfrac{5}{7}\cdot\dfrac{1}{5}-\dfrac{8}{9}$

$=\dfrac{6}{7}+\dfrac{1}{7}-\dfrac{8}{9}$

$=\dfrac{7}{7}-\dfrac{8}{9}$

$=1-\dfrac{8}{9}$

$=\dfrac{1}{9}$

$\dfrac{1}{4}+\dfrac{3}{4}(\dfrac{-1}{2}+\dfrac{2}{3})$

$=\dfrac{1}{4}+\dfrac{3}{4}\cdot\dfrac{1}{6}$

$=\dfrac{1}{4}+\dfrac{1}{8}$

$=\dfrac{3}{8}$