1, according to the arrangement of numbers, the difference between the first and third numbers is 3, and the difference between the second and fourth numbers is 3, so according to the arrangement rules of numbers, it should be 369, 147, and the brackets should be 9;
2. Use addition and subtraction to solve the problem. The first and third graphic boxes are outside, and the second and fourth graphic boxes are inside. If there are the same conditions, the difference between subtracting and canceling the box is 3 (this is the relationship between triangle and circle, and whether triangle and circle are added or subtracted is triangle plus or minus circle =3), so the brackets should be 3;
As for other answers, such as 2 or 7, I won't go into details here.
Personally, I think there is no standard answer to this question, and there is no need to have a standard answer.
Look at the tip in the upper right corner: "Think about it and tell me why." Let's think about whether this hint is not standard, and whether the standard expression of words in math problems should be like this: "Think about it and put the correct numbers in brackets."
Therefore, I personally think that this topic is not about pure mathematics (first-year mathematics is just a topic), but about students' creative thinking and training students' multi-angle thinking ability. No matter what the result is, as long as the reasoning process is reasonably related to the result, that is the correct answer.
In a word, the result is not important, but the process.
Personal opinion, for reference only.