\(C=\dfrac{12}{35}-\dfrac{-6}{7}+\dfrac{18}{14}:\dfrac{6}{7}-\dfrac{-2}{5}-1\)
\(=\dfrac{12}{35}+\dfrac{30}{35}+\dfrac{9}{7}\cdot\dfrac{7}{6}+\dfrac{2}{5}-1\)
\(=\dfrac{6}{5}+\dfrac{2}{5}-1+\dfrac{3}{2}\)
\(=\dfrac{3}{5}+\dfrac{3}{2}=\dfrac{21}{10}\)