a) $\frac{-3}{4}$ + $\frac{3}{7}$ + $\frac{-1}{4}$ + $\frac{4}{7}$
=($\frac{-3}{4}$ + $\frac{-1}{4}$ ) + ( $\frac{3}{7}$ + $\frac{4}{7}$ ) + $\frac{4}{9}$
= $\frac{-4}{4}$ + $\frac{7}{7}$ + $\frac{4}{9}$
= -1 + 1 + $\frac{4}{9}$
= 0 + $\frac{4}{9}$ = $\frac{4}{9}$
b) $\frac{-7}{9}$ . $\frac{4}{11}$ + $\frac{-7}{9}$ . $\frac{7}{11}$ + 5$\frac{7}{9}$
= $\frac{-7}{9}$ . ( $\frac{4}{11}$ + $\frac{7}{11}$ ) + 5$\frac{7}{9}$
= $\frac{-7}{9}$ . $\frac{11}{11}$ + 5$\frac{7}{9}$
= $\frac{-7}{9}$ .1 + 5$\frac{7}{9}$
= $\frac{-7}{9}$ + 5 + $\frac{7}{9}$
= ( $\frac{-7}{9}$ + $\frac{7}{9}$ ) + 5
= 0+ 5 = 5
c) ($\frac{21}{31}$ + $\frac{2013}{6039}$ ) - ($\frac{44}{53}$ - $\frac{10}{31}$ ) - $\frac{9}{53}$
= $\frac{21}{31}$ + $\frac{1}{3}$ - $\frac{44}{53}$ + $\frac{10}{31}$ - $\frac{9}{53}$
= $\frac{21}{31}$ + $\frac{1}{3}$ + $\frac{-44}{53}$ + $\frac{10}{31}$ + $\frac{-9}{53}$
= ( $\frac{21}{31}$ + $\frac{10}{31}$ ) + ( $\frac{-44}{53}$ + $\frac{-9}{53}$ ) + $\frac{1}{3}$
= 1 + (-1) + $\frac{1}{3}$
= 0 + $\frac{1}{3}$ = $\frac{1}{3}$
