Part A: 216 students/ 12 classrooms= 18 students: 1 classroom.
Part B: 104 students/ 4 classrooms= 26 students: 1 classroom.
The average ratio of students to classrooms in both school is:
[(18 students: 1 classroom)+ (26 students: 1 classroom)] /2= 22 students: 1 classroom.
26 students - 22 students= 4 students.
There are 4 students who would have to transfer from School B to School A for the ratios of students to classrooms at both schools to be the same, which is 22 students: 1 classroom.
Hope this helps~