2x+6 is the base
Then the equation is logarithm of 144 on basis 2x + 6 = 2
Then [2x + 6]^2 = 144
Now expand the square binomial
4x^2 + 24x + 36 = 144
4x^2 + 24x + 36 - 144 = 0
4x^2 + 24x - 108 = 0
Divide by 4
x^2 + 6x - 27 = 0
Factor: (x + 9 ) (x - 3) = 0
x = -9 and x = 3
The only valid is x = 3, because x = -9 yields 2x + 6 = - 12 and the logarithm function cannot have negative basis.
Then the answer is x = 3.