We are told that, out of 30 students of Mary's class, 6 of them work after school.
Thus the ratio of students who work after school to the total students is
[tex]\frac{6}{30}=\frac{1}{5}[/tex]If there are 525 students in the school, the number of students who work after school should be 1/5 of this number, thus the number of students who work after school should be;
[tex]\frac{1}{5}\times525=105[/tex]Thus it should be 105 students.
