Explanation:
for a plane defined as
Ax + By + Cz + D = 0
(A, B, C) is the normal vector (90° with the plane).
so, we know with the given normal vector (-6, 3, -3) that
A = -6
B = 3
C = -3
we are only missing D.
for that we use the given point (7, -4, 5) :
-6×7 + 3×-4 + -3×5 = D
-42 - 12 - 15 = D
-69 = D