Given the system of equations $\left\{ \begin{array} { l } k x + ( k + 1 ) y + z = 0 \\ - x + k y - z = 0 \\ ( k - 1 ) x - y = - ( k + 1 ) \end{array} \right.$ it is requested:
a) (2 points) Discuss the system according to the values of the real parameter k.
b) ( 0.5 points) Solve the system for $\mathrm { k } = - 1$.