a) $A=\dfrac{-5}{7}+\dfrac{3}{4}+\dfrac{-1}{5}+\dfrac{-2}{7}+\dfrac{1}{4}$;

b) $B=-\dfrac{3}{31}+\dfrac{-6}{17}+\dfrac{1}{25}+\dfrac{-28}{31}+\dfrac{-11}{17}+\dfrac{-1}{5}$;

c) $C=\dfrac{-1}{3}+\dfrac{2}{5}+\dfrac{-2}{3}+\dfrac{-3}{5}+\dfrac{1}{5}$.

a) $A=\dfrac{-16}{19}+\dfrac{-5}{46}+\dfrac{-7}{25}+\dfrac{7}{25} +\dfrac{5}{46}+\dfrac{35}{19}$;

b) $B=\dfrac{-2}{11}+\dfrac{52}{264}+ \dfrac{-1}{6}+\dfrac{5}{24}+\dfrac{3}{22} +\dfrac{-7}{8}$.

a) $A=\Big[ 4\dfrac{5}{37}+\Big(-3\dfrac{4}{5}\Big)+8\dfrac{15}{29}\Big]+\Big(-3\dfrac{5}{37}+6\dfrac{14}{29} \Big)$;

b) $B=-13\dfrac{3}{4}+\Big(3\dfrac{2}{7}+8\dfrac{3}{4} \Big)$;

c) $C=\Big(9\dfrac{3}{13}+5\dfrac{2}{9} \Big)+\Big(-7\dfrac{3}{13}\Big)$.