Which expression is equivalent to the one below?

The radius is 8.5

Step-by-step explanation:

Mathematically, the radius of a circle is the distance from the center of the circle to its circumference

Thus, as we have here;

The two marked lengths are radii of the inner inscribed circle and this means that they are equal in length

thus;

x + 6 = 5x-4

5x - x = 6 + 4

4x = 10

x = 10/4

x = 2.5

Now, to get the radius length, substitute the value of x in any of the lengths

from x + 6

2.5 + 6 = 8.5