Ois the center of the given circle. the measure of angle o is 128°. the diagram is not drawn to scale. assuming that lines that appear to be tangent are tangent, what is the value of x?

We know that

The measure of the external angle is the semi difference of the arcs that it covers.
so
see the picture attached to better understand the problem

m AB=128°--------> by central angle
m ACB=360°-128°-----> m ACB=232°
∠x=(1/2)*[m ACB-m AB]
∠x=(1/2)*[232-128]-----> ∠x=(1/2)*104°-----> ∠x=52°

the answer is
∠ x is 52°