20.计算:(能简算的简算)
(1)$\frac{9}{11}$×$\frac{7}{15}$×$\frac{11}{3}$
(2)$\frac{7}{8}$×$\frac{1}{5}$+4.125÷5
(3)$\frac{7}{8}$×$\frac{5}{9}$+$\frac{1}{8}$×$\frac{4}{9}$
(4)( $\frac{4}{9}$-$\frac{1}{3}$+$\frac{5}{6}$)×18
(5)$(0.75-\frac{3}{16})×(\frac{2}{9}+\frac{1}{3})$
(6)$6÷\frac{6}{7}-\frac{6}{7}÷6$.