a)$\frac{3}{5}$ +$\frac{-4}{15}$
=$\frac{9}{15}$ + $\frac{-4}{15}$
=$\frac{5}{15}$
=$\frac{1}{3}$
b)$\frac{-1}{3}$ + $\frac{2}{5}$ +$\frac{2}{15}$
= $\frac{-5}{15}$+ $\frac{6}{15}$ +$\frac{2}{15}$
=$\frac{1}{5}$
c)$\frac{-3}{5}$+$\frac{7}{21}$+$\frac{-4}{5}$+$\frac{7}{5}$
=$\frac{-3}{5}$+$\frac{1}{3}$+$\frac{-4}{5}$+$\frac{7}{5}$
=$\frac{-4}{15}$+$\frac{3}{5}$
=$\frac{-4}{15}$+$\frac{9}{15}$
=$\frac{5}{15}$
=$\frac{1}{3}$
d)$\frac{2}{7}$+$\frac{1}{9}$+$\frac{3}{7}$+$\frac{5}{9}$+$\frac{-5}{6}$
=($\frac{2}{7}$+$\frac{3}{7}$)+($\frac{1}{9}$+$\frac{5}{9}$)+$\frac{-5}{6}$
=$\frac{5}{7}$+$\frac{2}{3}$+$\frac{-5}{6}$
=$\frac{90}{126}$+$\frac{84}{126}$+$\frac{-105}{126}$
=$\frac{69}{126}$
=$\frac{23}{42}$
