Final answer:
After rotating a 7-inch square piece of plywood 90 degrees counterclockwise, the length of each side remains 7 inches because rotation does not change side lengths.
Step-by-step explanation:
When Halley cuts a 7-inch square piece of plywood and rotates it 90 degrees counterclockwise, the length of each side of the plywood remains unchanged. A 90-degree rotation does not alter the lengths of the sides but only changes the plywood's orientation. Therefore, the length of each side of the plywood after rotation is still 7 inches.