title: whereto write this code correctly
body: <p>new to c#... I got this question and got the answer , but I am confused as to where the answer should be written  (in main or in the class itself)</p>
  
  <p><strong>Question:</strong>
  <em>Given an instance circle of the following class:</em></p>
  
  <pre><code>public sealed class Circle 
  {
    private double radius;
  
    public double Calculate(Func&lt;double, double&gt; op) {
      return op(radius);
    }
  }
  </code></pre>
  
  <p>write code to calculate the circumference of the circle, without modifying the Circle class itself.</p>
  
  <p><strong>the answer is:</strong> </p>
  
  <pre><code>circle.Calculate(r =&gt; 2 * Math.PI * r);
  </code></pre>
  
  <p>also what exactly the meaning of <code>=&gt;</code> in this case </p>