Puzzle ZCSC 

Workings

Hint
Look at the letter positions in the alphabet.

Answer
R.

If you take the alphabetic positions of each letter in a row, the total is always 56.

Double-Checking
Y + G + W + A = 25 +  7 + 23 +  1 = 56
K + L + R + O = 11 + 12 + 18 + 15 = 56
Z + J + P + D = 26 + 10 + 16 +  4 = 56
V + F + T + H = 22 +  6 + 20 +  8 = 56