You can factor this treating (x+6) as the variable.

(x+6)^2 - 4(x+6) - 12 = 0

((x+6) - 6)((x+6) + 2) = 0 (factors of -12 that add to -4 are -6 and 2.)

(x)(x+8) = 0

The solutions are {-8, 0}.

(x+6)^2 - 4(x+6) - 12 = 0

((x+6) - 6)((x+6) + 2) = 0 (factors of -12 that add to -4 are -6 and 2.)

(x)(x+8) = 0

The solutions are {-8, 0}.