Observe the given diagrams carefully.
Scale factor is a concept used in dilation of figures.
Here the dilated figure is a rectangle.
So the scale factor is defined as the ratio of their linear measurements.
Then the scale factor (SF) of rectangle A to rectangle, will be given by the ratio of any linear measurement of rectangle A to the corresponding linear measurement of rectangle B,
Thus, the required scale factor is 1/5 or 0.2.