From the first picture and the second picture, we can see that the circles and squares represent 1 and 2 respectively. As for which is 1 and which is 2, we don't know yet.

However, it is found that the intersecting part of the graph is subtraction, the disjoint part is addition, and there is no negative number in the first grade of primary school.

So, the square is 1 and the circle is 2.

According to the above law, the third picture directly draws the conclusion that the triangle is 5.

The fourth number is 5- 1, which proves the above law.

So the final answer is 7, because there is no intersection, so it is addition, while the triangle is 5 and the circle is 2.

This level is already a civil servant exam, and it is a bit embarrassing to do it in the first grade of primary school.