$\frac{6}{7}$ + $\frac{5}{8}$ : 5 - $\frac{3}{6}$ . (-2)²
= $\frac{6}{7}$ + $\frac{5}{8}$ . $\frac{1}{5}$ - $\frac{1}{2}$ . 4
= $\frac{6}{7}$ + $\frac{1}{8}$ - 2
= $\frac{48}{56}$ + $\frac{7}{56}$ - $\frac{112}{56}$
= $\frac{48 + 7 - 112}{56}$
= $\frac{-57}{56}$