a)
\(\frac{-3}{7}-(\frac{2}{3}-\frac{3}{7})\)
=\(\frac{-3}{7}-\frac{5}{21}\)
=\(\frac{-2}{3}\)
b)
\(\frac{2}{15}:(\frac{1}{3}.\frac{4}{5}-\frac{1}{3}.\frac{6}{5})\)
=\(\frac{2}{15}:[\frac{1}{3}.(\frac{4}{5}-\frac{6}{5})]\)
=\(\frac{2}{15}:(\frac{1}{3}.\frac{-2}{5})\)
=\(\frac{2}{15}:\frac{-2}{15}\)
=-1