The volumes of three kinds of materials are in the ratio 4 : 5 : 7 and the masses of equal volumes of the three materials are in the ratio 7 : 3 : 5. If they are mixed to form a material of 78 kg then the mass of the 2^nd material in the mixture is

18 kg

15 kg

12 kg

9 kg

The volumes of three kinds of materials are in the ratio 4 : 5 : 7 and the masses of equal volumes of the three materials are in the ratio 7 : 3 : 5. If they are mixed to form a material of 78 kg then the mass of the 2nd material in the mixture is