Proportion of students in grade 4.6 = 1: 7 = 7: 6.
Level 4, 5 and 6 linkage = 28: 30: 24.
Level 4: 615 ÷ (28+30+24) × 28 = 210 (person)
Grade 5: 6 15 ÷ (28+30+24) × 30 = 225 (person)
Grade 6: 615 ÷ (28+30+24) × 24 =180 (person)
A: There are 2 10 students in Grade 4, 225 students in Grade 5 and 0/80 students in Grade 6.