Oil and kerosene are present in ratio of 5 : 7 in a liquid. Few litres of mixture is replaced with petrol. Ratio of oil : kerosene: petrol in the mixture is 35 : 49 : 18 respectively. Amount of oil removed from mixture is 21 litres less than that of petrol added to the mixture and amount of oil removed is 6 litres less than that of difference mentioned between petrol and oil. Petrol is replacing the mixture removed hence; quantity of mixture is not changing. What is the difference between quantity of kerosene in old mixture and amount of oil in new mixture?