We can see that the value for the segment AC is AX + XC ---> AC = 8.1 + 8.1 ---> AC = 16.2.
We can obtain this result if we use the Angle bisector theorem. It says that an angle bisector of a triangle will divide the opposite side of the angle into two segments that will be proportional to the other sides of the triangle.
In this case, we have that both sides, AB and CB are congruent, therefore, we have: