To determine the scale factor used to dilate polygon ABCD to A′B′C′D′, we can compare the corresponding side lengths.
The distance between A(1, 1) and B(3, 1) is 2 units, and the distance between A′(3, 3) and B′(9, 3) is 6 units, so the horizontal side has been scaled by a factor of 6/2 = 3.
Similarly, the distance between A(1, 1) and D(1, 2) is 1 unit, and the distance between A′(3, 3) and D′(3, 6) is 3 units, so the vertical side has been scaled by a factor of 3/1 = 3.
Since both scaling factors are equal to 3, the overall scale factor used to dilate the polygon is 3. Answer: 3.