Question

How to find the missing length indicated

Answer 1

x = diameter
radius r = 9.9 + 5.5 = 15.4
x = 15.4 (2) = 30.8

answer
x = 30.8

Answer 2

I think you are trying to find the diameter of the circle, where x is.

9.9+5.5=15.4

(that line with 9.9 is the radius)

The radius is half the diameter, so:

15.4+15.4= 30.8

30.8 is x or the diameter.

I hope this helps!
~kaikers