Sum of all nos
In first row=31.
In second row=26 (31-5)
In third row=23 (26-3)
In fourth row=21 (23-2)
He re the no which is subtracting from the sum is decreading by 2,1,0..so next we have to subtract 2-0=2 from the sum.
Fifth row shold be 21-2=19
So the ans should be 5.