Rekha is preparing a special fruit juice by mixing mango pulp and water. She finds that the best taste is obtained when the two are mixed in the ratio \(3:4\).
Based on this situation, answer the following:
1. If Rekha uses 9 litres of mango pulp, how many litres of water should she add to maintain the same ratio?
2. If she prepares 21 litres of the mixture, find the quantity of mango pulp (in litres).
3. If she prepares 21 litres of the mixture, find the quantity of water (in litres).
4. If he accidentally adds 8 litres of water, how much mango pulp (in litres) must she add to maintain the ratio?