Guess poems, high school students.

I guess it is 9, because the first two pictures are a circle in a square and a square in a circle, the third and fourth pictures are a triangle in a square and a square in a triangle, and the fifth picture is a circle in a triangle, so the sixth picture should be a triangle in a circle. So we went to see it in pairs. The first one in the first group is 3, and the first one in the second group is 6, so I guess the first one in the third group is 9.