According to the quantity equation if real GDP=15, velocity of money is 5, price level=4, money supply is: 12 d. 24 e. Posted on August 2, 2021 | by wp 45. According to the quantity equation if real GDP=15, velocity of money is 5, price level=4, money supply is: a. 3 b. 3.75 c. 12 d. 24 e. none of the above