what is the value of x to the nearest tenth?

13.4

5.5

4.9

12.0

'x' is a radius of the circle.

What happens when you connect the center of the circle
to one end of the chord ?  The line that you drew is another
radius, so it has the same length as 'x'.

You also create a right triangle.  One leg is 6, and the other leg is 12.
The radius that you drew is the hypotenuse of the triangle, so its
length is

          √(6² + 12²)  =  √(36 + 144)  =  √180  =  13.4164...  (rounded)