According to the given image, x is the radius of the circle.
So, we can find x using Pythagorean's Theorem in the following right triangle.
Where x is the hypothenuse.
[tex]\begin{gathered} x^2=5.3^2+4^2 \\ x=\sqrt[]{28.09+16} \\ x=\sqrt[]{44.09}\approx6.6 \end{gathered}[/tex]