Two solutions A and B of acid and water contain acid and water in the ratio 7 ∶ 9 and 5 ∶ 3, respectively. A and B are mixed in the ratio x ∶ y. If the ratio of acid and water in the resulting solution is 9 ∶ 7, then x ∶ y is:
1
4 ∶ 5
2
2 ∶ 3
3
1 ∶ 2
4
3 ∶ 4