When the distance between them goes from 8 ft to 12 ft, it is 1.5 times what it was. Then the force will be multiplied by the inverse of the square of this:
(75 lb)×1/(1.5²) = 75/2.25 lb = 33 1/3 lb
At 12 feet apart, the attraction force is 33 1/3 pounds.
