The puzzle's logic is

1st figure : (9-7) + (8-5) = 2 + 3 = 5

2nd figure : (15-6) + (11-2) = 9 + 9 = 18

similarly, 3rd figure : (9-6) + (17-5) = 3 + 12 = 15.

From all the hints given, 

only 042 satisfies and it unlocks the key.

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From statement B, 

As the value of L = 0, the value of KL = 0.

Hence only statement B is sufficient.