Final answer:
The number of side units in each square would be three.
Step-by-step explanation:
The diagram is not provided, so we cannot determine the number of side units if there were nine squares. However, if we assume that each square has the same number of side units, we can find the number of side units in a single square by taking the square root of the total number of squares. In this case, the square root of nine is three, so there would be three side units in each square.