Вычислите: 27/42+(12/42-6/42)-12/42.

\[\frac{27}{42} + \left( \frac{12}{42} - \frac{6}{42} \right) - \frac{12}{42} =\]

\[= \frac{27}{42} + \frac{6}{42} - \frac{12}{42} = \frac{21}{42} = \frac{1}{2}.\]