How many kg of rice costing ₹42 per kg should be mixed with kg rice costing ₹50 per kg so that by selling the mixture at₹ 53.10 per kg, there is a gain of 18%?

A and B are solutions of acid and water. The ratio of water and acid in A and B are 4 : 5 and 1 : 2, respectively. If x literes of A is mixed with y litres of B, then the ratio of water and acid in the mixture becomes 8 : 13. What is x : y ?