Let the number of boys in class IX A be x and number of girls be y
Average amount given by girls = Rs. 200
(a) Total amount donated by girls = Rs. 4400
Number of girls in class IX A = Total Amount/ Avg-amount
= 4400/200
Number of Girl (y) in class IX A = 22
Number of boys (x) in class IX A = Total Amount / Avg-amount
= 4200/150
Number of boys (x) in class IX A = 28
Total student in class IX A (x + y) = 22 + 28
= 50
(b) Avg. amount given by the student of class IX A