Answer:
x = 56
See below if you don't understand!
Explanation:
We are told that AC = 28, we can also see that the lines coming out from the centre of the circle are parallel. The intersect between these lines and the line AB is at right angles
This similarity between both sides of the circle give us the answer to our question as we can see that both have symmetrical dimensions. This means that we just have to double 28 to get our answer x = 56
Hope this helps, have a lovely day! :)