12N
Explanation:
By Newton second law force is the product of the mass of the object times it's acceleration. That makes it
the old price per ounce is c/4.
the new price per ounce is c/3.6.
the ratio of the old price to the new one is
(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form