Dun understand why Add when it should be Substrate

Question

Dear experts,

 

I have this multi-cast delegate which I am having problem understand:

 

delegate void M(int x, int y);

public class Oper
{
  public static void Add(int x, int y)
  {
   Console.WriteLine("{0} + {1} = {2}", x, y, x+y);
 }

 public static void Sub(int x, int y)
{
Console.WriteLine("{0} + {1} = {2}", x, y, x+y);
}

public class CSharpApp
{
 static void Main()
{
M del = new M(Oper.Add);
del += new M(Oper.Sub);
del(6,4);

del -= new M(Oper.Sub);
del(2,8);
}
}

I would like to know why the output for del(2,8) is 10 instead of 2 - 8 which is -6.