$=\frac{21}{42}+\frac{7}{42}+\frac{1}{42}+(\frac{1}{12}+\frac{1}{20}+\frac{1}{30})$
$=\frac{29}{42}+(\frac{1}{12}+\frac{1}{20}+\frac{1}{30})$
$=\frac{29}{42}+(\frac{5}{60}+\frac{3}{60}+\frac{2}{60}$
$=\frac{29}{42}+\frac{1}{6}$
$=\frac{29}{42}+\frac{7}{42}$
$=\frac{36}{42}=\frac{6}{7}$