Plug in the value for 'n = 2' into '-6n-2n=16' and you will get:

-6*2 - 2*2 = -12 - 4 = - 16

and this is different than '16' thus 'n = 2' is not the solution.

Then, plug in the value for 'n = - 2' into '-6n-2n=16' and you will get:

-6*(-2) - 2*(-2) = 12 + 4 = 16

so the solution is indeed 'n = -2'.