'AEIOU' is written as 'TNHDZ'
The above code following 2 conditions
1. character-1
2. Firs position is replaced with last position
A-1= Z and placed in last
E-1= D placed in second last
I-1=H placed in third last
O-1=N placed in fourth last
S-1=T placed in first position

The same order will follow for 'BFJPV'
B-1= A placed in last
F-1=E is placed in second last
J-1=I is placed in third last
P-1=O is placed in fourth last
V-1=U is placed in first position.

PAN = 31 → (1)
PAR = 35 → (2)
PAT = 37
From (1) & (2), PA = 3; Difference between N to R is (5 - 1) = 4 i.e., no. of alphabets between N & R such as no. of alphabets between R and T is ‘2’ then ‘7’ is correct number. Difference between 7 and 5 is 2.

5 + 4 + 7 + 2 = 18 = (1 + 8) = 9; 6 + 3 + 4 + 2 = 15 = (1 + 5) = 6
7 + 5 + 8 + 4 = 24 = (2 + 4) = 6; 9 + 2 + 3 + 6 = 20 = (2 + 0) = 2