using System;

​

//Given an instance circle of the following class:

​

public sealed class Circle 

{

  private double radius;

  public double Calculate(Func<double, double> op) 

  {

    return op(radius);

  }   

}

​

​

​

//write code to calculate the circumference of the circle, without modifying the Circle class itself.

​

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public class Program

{

  public void Main()

  {

      var rad = 50;

      var circle = new Circle();

      var circumference = circle.Calculate(r => { return 2 * Math.PI * rad; });

      Console.WriteLine("Circumference is "+ circumference.ToString("##.##"));

  }

}   

​