My son decided his homework as follows:
6 + 13 = 22 (≡ 16)
At first I thought that my son made a mistake. But he was right.
I propose to you to solve the two examples to find the cache:
1155 + 554 = abcd (≡ KLM)
626 + 423 = efgh (≡ NOP)
The cache is located at coordinates
N50 23.KLM E30 30.NOP
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You can validate your puzzle solution with certitude.
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