(3 / 8x) - (1 / (3x + 6)) = 1 / (6x)
Note that x cannot be 0 or -2, or we will have zero in the denominator of some of the terms.
[3(3x + 6) - (1)(8x)] / [(8x)(3x + 6)] = 1 / 6x
[9x + 18 - 8x] / [(24x)(x + 2)] = 1 / 6x
[x + 18] / [(24x)(x + 2)] = [4(x + 2)] / [(24x)(x + 2)]
x + 18 = 4(x + 2)
x + 18 = 4x + 8
4x - x = 18 - 8
3x = 10
x = 10 / 3