Given the system $\left\{ \begin{array} { c } ( a + 1 ) x + 4 y = 0 \\ ( a - 1 ) y + z = 3 \\ 4 x + 2 a y + z = 3 \end{array} \right.$, find:\ a) ( 1.25 points) Discuss it as a function of the parameter $a$.\ b) ( 0.5 points) Solve it for $a = 3$.\ c) (0.75 points) Solve it for $a = 5$.