EDIT: this may be an scam attempt but i can not be sure because i am not familiar with ETH under the hood that much.
it seems to be a riddle!
if you get the answer correctly then you can create a transaction with the answer which is basically a script that runs with keccak256 hash function which will then be checked against the output that was created and if they match then the signature will be valid!
the answer to the riddle is obvious, so the only question remaining now is "how to spend a contract in Ethereum"...