$\begin{array}{*{20}{l}}
{\overrightarrow {BA} {\rm{ \;}} = \left( { - 2; - 8} \right),\overrightarrow {AC} {\rm{ \;}} = \left( { - 3;3} \right),\overrightarrow {BC} {\rm{ \;}} = \left( { - 1;11} \right)}\\
{\cos B = \frac{{\overrightarrow {BA} .\overrightarrow {BC} }}{{BA.BC}} = \frac{{\left( { - 2} \right).\left( { - 1} \right) + \left( { - 8} \right).11}}{{\sqrt {{2^2} + {8^2}} .\sqrt {{1^2} + {{11}^2}} }} = \frac{{ - 86}}{{\sqrt {8296} }}}\\
{ \Rightarrow \hat B \approx {{160}^0}}\\
{b)\overrightarrow {{n_{AB}}} {\rm{ \;}} = \left( {4; - 1} \right)}\\
{{\rm{\;}} \Rightarrow pt\,AB:4\left( {x - 6} \right) - 1\left( {y + 2} \right) = 0}\\
{ \Leftrightarrow 4x - y - 26 = 0}\\
{\overrightarrow {{n_{AC}}} {\rm{ \;}} = \left( {1;1} \right)}\\
{pt\,\,AC:x{\rm{\;}} - 6 + y + 2 = 0}\\
{{\rm{n}} \Leftrightarrow x + y - 4 = 0}\\
{\overrightarrow {{n_{BC}}} {\rm{ \;}} = \left( {11;1} \right)}\\
{pt\,\,BC:11\left( {x - 3} \right) + y - 1 = 0}\\
{ \Leftrightarrow 11x - 33 + y - 1 = 0}\\
{{\rm{\;}} \Leftrightarrow 11x + y - 34 = 0}
\end{array}$
