Explanation:

- Two years ago, B was 7 years old (since B is currently 9 years old).

- At that time, A was three times B's age, making A 21 (3 times 7).

- Currently, A is 23 years old (21 + 2 years).

- The goal is to find when A's age will be double B's age.

- Suppose this occurs in x years. The equations are:

- A's future age = 23 + x

- B's future age = 9 + x

- The condition is: 23 + x = 2(9 + x).

- Solving:

- 23 + x = 18 + 2x

- 23 - 18 = 2x - x

- 5 = x

- After 5 years, A's age will be double B's age.

- Correct Answer: Option 4, 5 years.