// remove the specified brick from this level's collection
 public void DeleteBrick(Brick brick)
 {
     if (Bricks.Contains(brick))
     {
         Bricks.Remove(brick);
         Changed = true;
     }
 }
 // add a new brick to the level, given the coordinate
 // of the a top, left corner, knowing the width and
 // height of all bricks on this level
 public Brick AddBrick(int x, int y, int hits)
 {
     Brick brick = null;
     if (x >= 0 && y >= 0)
     {
         brick = new Brick();
         brick.X = x;
         brick.Y = y;
         brick.HitsToClear = hits;
         Bricks.Add(brick);
         Changed = true;
     }
     return brick;
 }