Solution:Let the quantity of milk in the initial mixture = 11x
And the quantity of water in the initial mixture = 4x
(11x - 30 × 11/15)/(4x - 30 × 4/15 + 33) = 2/1
(11x - 22) = (4x + 25) × 2
11x - 22 = 8x + 50
x = 24
Required initial quantity = (11 + 4) × 24 = 360 liters