How many water molecules are present in 54 gram of water?
We assess the molar quantity of water in the usual way...
And so (finally!) we take the product...
These can be figured out using the concept of moles and molecular weight. I have attached a video that provides a good explanation.
Now you have all the information needed to solve the problem.
You start out with 54 grams of water. You want to convert that into molecules, but how can you do that? You can't go directly from grams to molecules because there is no easy unit conversion. However, you can go from grams to moles using
From there, you can go from moles to molecules using
A T chart is useful for this kind of problem.
Notice when you apply this T chart, the units cancel out, leaving molecules in the final answer, which is the correct units.
Now actually multiply everything out
You are left with