In a school there are 458 more girls than boys. If there are 692 girls how many pupils are there in that school?
here are three grades in that school. In each grade, there are three classes. Each class has about 30 students. So...

There are 3 grades in the school.
Each grade has 3 classes.
Each class has 30 students.

3 x 3 x 30 = 270

There are 270 students in the school.