Explanation:

Let's break it down:

- The speed ratio of the stream to the speed of the first boat is 4:7. This means, for every 4 units of speed of the stream, the first boat has 7 units of speed.

- The speed ratio of the stream to the speed of another (second) boat is 2:5. This signifies that for every 2 units of stream speed, the second boat has 5 units of speed.

- To find the ratio of the first boat to the second boat, we equate the stream part:

- For the first boat, let stream speed = 4x and boat speed = 7x.

- For the second boat, let stream speed = 2y and boat speed = 5y.

- Since the stream speed must be consistent, equate them: 4x = 2y. This makes x = y/2. Substitute back:

- First boat speed: 7x = 7(y/2) = 7y/2

- Second boat speed: 5y

Thus, the ratio of the speed of the first boat to the second boat is (7y/2) : 5y = 7 : 10.

- Correct Answer: Option 2, 7:10