Answer:
The negative solution is -2
Explanation:
Let the number be x
From the question we can deduce the equation below;

Solving the quadratic equation by factorization;


the factors of the quadratic equation are -8 and 2

x(x-8)+2(x-8)=0
(x+2)(x-8)=0
Therefore, x = -2 or 8
The negative solution is -2.
PROOF;

[-2]^2 - 16 = 6(-2)
4 - 16 = -12
-12 = -12