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
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Puzzle 3
I have a bottle and a straw which cost me 60 pence. The bottle cost 10 pence more than the straw. What does each item cost?