From tank T₁ containing 54 litres of a mixture of chemical and aqua in the ratio of 8 : 1, 18 litres of the mixture is taken out and poured into tank T₂ in which the ratio of chemical to aqua is 3 : 1. If the difference between total chemical and total aqua in tank T₂ is 30 litres, then find the quantity of initial mixture in tank T₂.