Varshika drew \(6\) circles with different sizes. Draw a graph for the relationship between the diameter and circumference of each circle as shown in the table and use it to find the circumference of a circle when its diameter is \(6 \ cm\).
 
Diameter (\(x \ cm\)) \(1\) \(2\) \(3\) \(4\) \(5\)
Circumference (\(y \ cm\)) \(3.1\) \(6.2\) \(9.3\) \(12.4\) \(15.5\)
 
Ans:
 
This is a type of .
 
Proportionality constant .
 
Circumference of a circle when its diameter is \(6 \ cm=\) .