215, 258 and 301⇒ 215 = 5 × 43⇒ 258 = 2 × 3 × 43⇒ 301 = 7 × 43⇒ HCF = 43Number of students in each sections is = 43Number of sections in grade 4 = 215/43 = 5Number of sections in grade 5 = 258/43 = 6Number of sections in grade 6 = 301/43 = 7∴ MINIMUM number of sections = 5 + 6 + 7 = 18