Now, you obviously can't use the water of crystallization to dissolve your salts. I believe you're alowed to use pure water to do this, aren't you?
Before doing it, however, you must weight both salts: the pure and the impure.
You, then, dissolve them (all the salts you start from are lovely soluble) and, finally, you'll get a solid precipitate, depending on the experiment either a phosphate or a carbonate.
Weight that too and do your calculations (I don't think you need help with them, do you?).
It's easier to do than to describe.