Calculate the class interval of the required class.
 
Class
\(1\)
\(2\)
\(3\)
\(4\)
\(5\)
Interval
2.2 -  17.917.9 - 23.923.9 - 39.739.7 - 44.344.3 - 56.6
 
The class interval of class \(4\) is .