Answer:
 C = 4 
Explanation:
 Given : Given a circle with measures of (C, d, and r) and a circle with measures of (C', d', and r'). 
and 

We have to find the value of C when C' = 16 
Consider, The given circle with measures of (C, d, and r) and a circle with measures of (C', d', and r'). 
Since, Circumference of circle is directly proportional to the diameter of circle.
Thus, C ∝ d
and C' ∝ d'
Given 

Thus, 

Simplify , we have, 
C' = 16
 

Simplify, we get, 
 

Thus, C = 4