Equation: $$\log_a (x) + \log_a (x-4) = \log_a (x+6)$$
Progress
$$\log_a (x^2-4x) = \log_a (x+6)$$ $$x^2-5x-6=0$$
Delta
$$x1= 6$$
$$x2=-1$$
Equation: $$\log_a (x) + \log_a (x-4) = \log_a (x+6)$$
Progress
$$\log_a (x^2-4x) = \log_a (x+6)$$ $$x^2-5x-6=0$$
Delta
$$x1= 6$$
$$x2=-1$$
Your first step is correct. Now, if you search only real solutions, you have $$ x^2-4x=x+6 $$ can you solve? (be care to the the acceptability of the solutions).