The average height of a certain number of students in a group is 155.6 cm. If 12 students having an average height of 150.5 cm join the group and students having an average height of 159 cm leave the group, the average height of the students in the group will decrease by 34 mm . What is the number of students. initially, in the group?

A

30

B

25

C

40

D

20