\[\boxed{\text{4.\ 186}}\]
\[\textbf{а)}\ x = 6;\ \ y = 10:\]
\[\frac{6 + 10}{2} = \frac{16}{2} = 8 \rightarrow K(8).\]
\[\textbf{б)}\ x = - 4;\ \ y = - 6:\]
\[\frac{- 4 + ( - 6)}{2} = - \frac{10}{2} =\]
\[= - 5 \rightarrow K( - 5).\]
\[\textbf{в)}\ x = - 1;y = 7:\]
\[\frac{- 1 + 7}{2} = \frac{6}{2} = 3 \rightarrow K(3).\]