\(\frac{3}{8}.\frac{5}{7}+\frac{6}{8}.\frac{1}{14}+\frac{9}{8}.\frac{1}{21}\)
\(=\frac{3}{8}.\left(\frac{5}{7}+2.\frac{1}{14}+3.\frac{1}{21}\right)\)
\(=\frac{3}{8}.\left(\frac{5}{7}+\frac{1}{7}+\frac{1}{7}\right)\)
\(=\frac{3}{8}.1\)
\(=\frac{3}{8}\)