A chemical solution contains 30% water and 70% Alkali. What quantity of water should be added to 6 litres of solution so that the water content became 40%? (In litre)

Initial solution: 6 litres with 30% water = 1.8 litres water, 70% alkali = 4.2 litres alkali. Let x litres of water be added. New total volume = 6 + x litres. Water content becomes (1.8 + x) litres. We want water to be 40%: (1.8 + x)/(6 + x) = 0.4. Solving: 1.8 + x = 0.4(6 + x) = 2.4 + 0.4x. So x - 0.4x = 2.4 - 1.8, giving 0.6x = 0.6, therefore x = 1 litre. Adding 1 litre water makes the solution 7 litres with 2.8 litres water = 40%.