A quadratic is applicable here given
6n = n2 - 16
Set up the quadratic by subtracting 6n from both sides of the equation:
0 = n2 - 6n - 16
Factoring
(n - 8)(n + 2)=0
The negative solution is n = -2
Checking in the original set up we have
6(-2) = (-2)2 - 16
-12 = 4 - 16
-12 = -12
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