Missing letters puzzle 

Given series is A F Z U G L T _

Starts with A

A + 5 letters = F

go to end of alphabet= Z

Z - 5 letters = U

from F go one more to G + 5 letters = L

from U go one back to U, T - 5 letters = O

Second Method ::

Change the letters to their corresponding number.

A=1

B=2

C=3

...

Z=26

A F Z U G L T _

1 6 26 21 7 12 20 ?

Look at the pattern: the 1st and 3rd numbers = 27, 1+26

the 2nd and 4th numbers = 27, 6+21

the 5th and 7th numbers = 27,

so the 6 and 8th would also equal 27.

27 - 12 = 15,

so the letter is O.

HURRAYS.

13 x 2 = 26 => Z (opposite side)

12 x 2 = 24 => X (opposite side)

13 x 1 = 13 => M (opposite side)

12 x 1 = 12 => L (opposite side)

The Logic followed in the given puzzle is :

L x P = 12 x 16 = 192 (Alphabetical numbers of L & P)

P x T = 16 x 20 = 320 (Alphabetical numbers of P & T)

Similarly, K x () = 132 => () = 132/11 = 12 => L

Hence, the missing letter is L

The logic in the given puzzle is 

Addition of numeric values of corresponding letters in the first three figures gives respective corresponding letter in fourth figure. 

i.e, A = 1 , W = 23 , B = 2 => 2 + 1 + 23 =26 = 'Z'

Similarly, L = 12, K = 11 , A = 1 => 1 + 11 + 12 = 24 = 'X'

Here the missing letter is 'X'.