In the diagram shown, points A and B have been dilated from center O . |AB|=12 and |A′B′|=8 . A ray starts at point O and passes through points A prime and A. A second ray starts at O and passes through points B prime and B. Segments A prime B prime and A B are drawn between the rays. What is the scale factor r so that dilation from center O maps segment AB to segment A′B′ ?