(6) (1) $a=4$ (can

take any real value in $[-3,5]$)
(2) $-4 \leqslant a \leqslant 5$ (the left endpoint of $a$ can take 

any real value in $(-\infty,-3)$)
(6) Given $M=\{x|| x+1|+| x-3 |>8\}, P=\left\{x \mid x^{2}+(a-8) x-8 a \leqslant 0\}:$
(1) Find a value of $a$ that makes it a sufficient but not necessary condition for $M \cap P=\{x \mid 5<x \leqslant 8\}$;
(2) Find a range of values for $a$ that makes it a necessary but not sufficient condition for $M \cap P=\left\{\left.x\right|^{\prime} 5<x \leqslant 8\right\}$.