In a mixture of water and spirit water is 25%. When 15 litre water is added in the mixture percentage of water increased to 40%. Find the quantity of spirit in the mixture.

Let the initial mixture quantity be x liters. Water = 25% of x = 0.25x, Spirit = 75% of x = 0.75x. After adding 15 liters of water: New water = 0.25x + 15, Total mixture = x + 15. Given that water becomes 40%: (0.25x + 15)/(x + 15) = 0.4. Solving: 0.25x + 15 = 0.4x + 6, so 15 - 6 = 0.4x - 0.25x, giving 9 = 0.15x, therefore x = 60. Spirit = 0.75 × 60 = 45 liters. Option B is correct.