\(M=\frac{1}{-6}.\frac{1}{4}+\frac{1}{4}.\frac{1}{-5}+\frac{1}{-5}.\frac{1}{6}\)
\(M=\frac{1}{4}.\left(\frac{1}{-6}+\frac{1}{-5}\right)+\frac{1}{-30}\)
\(M=\frac{1}{4}.\frac{-11}{30}+\frac{1}{-30}\)
\(M=\frac{-11}{120}+\frac{-4}{120}\)
\(M=-\frac{1}{8}.\)