Explanation:

- Kulbhushan starts with 140 litres of juice that has 40% water.

- This means he has $0.4\times 140=56$ litres of water and 84 litres of syrup.

- He sells 30 litres of this juice.

- Therefore, the remaining juice equals 110 litres.

- The remaining water: $(56/140)\times 110=44$ litres.

- The remaining syrup: $(84/140)\times 110=66$ litres.

- An equal amount of syrup and water is added, and the water-to-syrup ratio becomes 3:4.

- Let $x$ be the quantity of water, also $x$ syrup is added.

- New water quantity = 44 + x

- New syrup quantity = 66 + x

- Given ratio: $(44+x)/(66+x)=3/4$

- Solving for $x$,

$$4(44+x)=3(66+x)$$

$$176+4x=198+3x$$

$$x=22$$

- Correct Answer: Option 4 - 22 litres