\(a,\dfrac{3}{5}.\dfrac{6}{7}+\dfrac{3}{7}:\dfrac{5}{3}-\dfrac{2}{7}:1\dfrac{2}{3}\)
\(=\dfrac{3}{5}.\dfrac{6}{7}+\dfrac{3}{7}.\dfrac{3}{5}-\dfrac{2}{7}.\dfrac{3}{5}\)
\(=\dfrac{3}{5}.\left(\dfrac{6}{7}+\dfrac{3}{7}-\dfrac{2}{7}\right)\)
\(=\dfrac{3}{5}.\dfrac{7}{7}\)
\(=\dfrac{3}{5}.1\)
\(=\dfrac{3}{5}\)
\(b,\dfrac{4}{9}:\left(\dfrac{1}{15}-\dfrac{2}{3}\right)+\dfrac{4}{9}:\left(\dfrac{1}{11}-\dfrac{5}{22}\right)\)
\(=\dfrac{4}{9}:\left(\dfrac{1}{15}-\dfrac{10}{15}\right)+\dfrac{4}{9}:\left(\dfrac{2}{22}-\dfrac{5}{22}\right)\)
\(=\dfrac{4}{9}:\left(-\dfrac{9}{15}\right)+\dfrac{4}{9}:\left(-\dfrac{3}{22}\right)\)
\(=\dfrac{4}{9}.\left(-\dfrac{15}{9}\right)+\dfrac{4}{9}.\left(-\dfrac{22}{3}\right)\)
\(=\dfrac{4}{9}.\left(-\dfrac{15}{9}-\dfrac{22}{3}\right)\)
\(=\dfrac{4}{9}.\left(-9\right)\)
\(=-4\)
