This diagram has a heading “Doing.” Underneath, the word “numberâ€™ is written, followed by an arrow pointing to a box. The box contains the operation “subtract 3.” From the box, a further arrow points to the answer 2. Under the first diagram there is a heading “Undoing.” The number 2 is followed by an arrow which points to a box. The box contains the operation “add 3.” From the box a further arrow points to the answer 5 (since 3 + 2 = 5).