Triangle ABC ​is transformed with the center of dilation at the origin.

Pre-image: △ABC with vertices A(2, 5), B(6, 10), C(9, −1)

Image: △A′B′C′ with vertices A′(0.5, 1.25), B′(1.5, 2.5), C′(2.25, −0.25)

What is the scale factor of the dilation that maps the pre-image to the image? Enter your answer in the box.