A drum contains a blend of three chemicals: P, Q, and R, in the ratio of 3:5:2. 30 litres of this blend are removed, and then 12 litres of chemical P and 8 litres of chemical Q are poured into the drum. If the resultant quantity of chemical Q is 20 litres more than the resultant quantity of chemical P, what was the initial total quantity of the mixture in the drum (in litres)?