Since Rita and Monika exchange places, so Rita's new position is the same as Monika's earlier position.This position is 17th from the right and 10th from the left.Number of girls in the row = (16 + 1 + 9) = 26.

Since Shilpa and Reena interchange positions, so Shilpa's new position is the same as Reena's earlier position.This position is 14th from the left (Shilpa's new position) and 17th from the right (Reena's earlier position).Number of girls in the row = (13 + 1 + 16) = 30.

Number of persons between Vijay and Jack = 48 - (14 + 17) = 17.Now, Mary lies in middle of these 17 persons i.e. at the eight position.So, number of persons between Vijay and Mary = 7.

Number of boys in the row = 10.Rohit's new position is 7th from the left or 4th from the right.His earlier position was two places to the right of his new position i.e. his earlier position was second from the right.

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Here A= C+3, 
D=B-4 
E= F-6, 
C= E+2 
F=D+3 
Now , Calculate the value of every term in respect to A.
Therefore, total number of articles.
= A+B+C+D+E+F
=A+(A+2)+(A-3)+(A-2)+(A-5)+(A+1)
=6A-7 
If A=8, then total numbers of items = 8x6-7=41 
If A=9, then total numbers of items = 9x6-7=47 
If A=10, then total numbers of items = 10x6-7=53

New rank from the end =47-21+1 = 27th

Therefore, Number of boys in the line =12+4-1 =15 
To have 28 boys in the line number of boys to be included = 28-15=13

When Rahul was shifted by three places towards his right side, then he occupies the middle position
.
Position from left end of the row
= 13-3 =10^th

Here, position of Rekha is 20th from right, which is occupied by Jaya after interchanging takes place and becomes 22nd from the left 
Therefore Total students in the row = (20+22)-1=41