The correct answer to this question is this one: "A. 28.5°"
Since AB = CB,
then, there are two angles that are the same:
angle CAB and angle ACB.
We need to get the value of x
4x - 3 + 2(x - 3) = 180
4x - 3 + 2x - 6 = 180
6x - 9 = 180
6x = 189
x = 31.5
So angle ACB would be,
mACB = x - 3
mACB = 31.5 - 3
mACB = 28.5