A bottle contains a mixture of two liquids A and B in the ratio 5: 3. If 6 litres of the mixture is replaced by 6 litres of liquid B, then the ratio of the two liquids becomes 5: 9. How much of the liquid A was there in the bottle? (Litres)

Let initial quantities be 5x and 3x. When 6 litres is removed, the ratio remains 5:3, so A removed = 5/8 × 6 = 3.75 L, B removed = 2.25 L. After adding 6 L of B, new A = 5x - 3.75, new B = 3x - 2.25 + 6 = 3x + 3.75. New ratio (5x - 3.75)/(3x + 3.75) = 5/9. Solving: 45x - 33.75 = 15x + 18.75, so 30x = 52.5, x = 1.75. Initial A = 5x = 8.75 litres.