If a mole is equivalent to 6.02x10^23 molecules, and a liter of water has about 55.5 moles of H20, how do I find the amount of molecules this is?

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(btw--thanks David for answering my last question)
But I don't think I quite understand this. (stupid doctor's appointment!)
Anyway, would I go about this--I don't need answers, just a good explanation. Thank you very much.