What should he do next in order to follow the steps of inquiry?
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Since he wonders, then according to the formal, methodical procedures of scientific inquiry, he should not go running off and trying stuff before he forms a hypothesis that can be tested.
In his mind, at some point, he should say to himself "Self ! It seems to me that if salt is added to water, it makes the water boil at a higher temperature than pure water does."
And only THEN, with this statement in mind, he's ready to design an experiment to test it.