5 kg of anhydrous are mixed with 20 kg of water. The mixture is then kept at until the maximum possible amount of has dissolved. Any undissolved is hydrated to form solid

. Calculate the mass of undissolved solid.

Data: Molecular Masses:

Solubility at : 20.7kg per 100 kg water.

I am bit confused on how to do this, as I am no sure what I am suppose to be working out? Is it the amount of copper sulphate in the hydrated solid?

Any help appreciated.

Thank you.