`a)` $\dfrac{6}{7}$+$\dfrac{5}{8}$ `: 5 -` $\dfrac{3}{16}$ `.` $(-2)^{2}$
`=` $\dfrac{6}{7}$`+`$\dfrac{5}{8}$ `.` $\dfrac{1}{5}$ `-` $\dfrac{3}{16}$ `.` `4`
`=` $\dfrac{6}{7}$`+`$\dfrac{1}{8}$ `-` $\dfrac{3}{4}$
`=` $\dfrac{48}{56}$`+`$\dfrac{7}{56}$ `-` $\dfrac{42}{56}$
`=` $\dfrac{13}{56}$
`b)` $\dfrac{2}{3}$ `+` $\dfrac{1}{3}$ `. [` $\dfrac{-4}{9}$ `+` $\dfrac{5}{6}$ `]` `:` $\dfrac{7}{12}$
`=` $\dfrac{2}{3}$ `+` $\dfrac{1}{3}$ `. [` $\dfrac{-16}{36}$ `+` $\dfrac{30}{36}$ `]` `:` $\dfrac{7}{12}$
`=` $\dfrac{2}{3}$ `+` $\dfrac{1}{3}$ `.` $\dfrac{7}{18}$ `:` $\dfrac{7}{12}$
`=` $\dfrac{2}{3}$ `+` $\dfrac{7}{54}$ `:` $\dfrac{7}{12}$
`=` $\dfrac{2}{3}$ `+` $\dfrac{6}{27}$
`=` $\dfrac{25}{27}$
