This problem is very similar to problem 3-66. Last time, you were told how many pieces
to add or subtract. This time, you will need to use the skills you have attained to determine
how best to reach −2 by adding two pieces.

Since the current value of this diagram is −2, you will need to add one negative piece
and one positive piece to keep the value of −2.

You already know the current value is −2. By only removing pieces from the picture,
how does −2 become 2? Think about this question, then proceed with the problem.