Answer:
These points are not coplanar
Explanation:
The first step in determining whether these four points are coplanar is to find three vectors from these points.
Let's call A(-9,8,1), B(10,-15,5),C(6,6,-12) an D(8,-4,-3).
From these points, we can find the following vectors:
AB = B-A = (10,-15,5)-(-9,8,1) = (19,-23,4)
AC = C-A = (6,6,-12)-(-9,8,1) = (15,-2,-13)
AD = D-A = (8,-4,-3)-(-9,8,1) = (17,-12,-4)
If the mixed product of the vectors AB, AC and AD is equal to zero, then these points are coplanar.
Since the mixed product between these points is not zero, these points are not coplanar.