4 You are given that if \(\mathbf { M } = \left( \begin{array} { r r r } 4 & 0 & 1
- 6 & 1 & 1
5 & 2 & 5 \end{array} \right)\) then \(\mathbf { M } ^ { - 1 } = \frac { 1 } { k } \left( \begin{array} { r r r } - 3 & - 2 & 1
- 35 & - 15 & 10
17 & 8 & - 4 \end{array} \right)\).
Find the value of \(k\). Hence solve the following simultaneous equations. $$\begin{aligned} 4 x + z & = 9
- 6 x + y + z & = 32
5 x + 2 y + 5 z & = 81 \end{aligned}$$