Em uma escola, estudam em tres periodos 1256 meninas e 1593 meninos. quantos alunos estudam nessa escola?

I will answer in English.

This can be translated to:

In a school, 1256 girls and 1593 boys study in three periods. how many students study at that school?

This means that we have a total of:

(1256 + 1593) students = 2849 students, divided in 3 periods.

So the total number of students in that school is 2849

And the number of students per period is:

2849/3 = 949.7

Because we can only have whole numbers here, we can say that in each period there are around 950 students.