Blue, Red and white paints are mixed in the ratio 2:1:3 by volume to get a paint mixture. If the total volume of the paint mixture was 9.6 litres, which of the following would give us the difference in the volumes of white and red paints used ?

a. (3 - 1) * 9.6

b. (3 - 1) / 9.6

c. [(3 + 1) / 6 ] * 9.6

d.  [(3 - 1) / 6 ] * 9.6