Water of Crystallisation

Hey guys, I was wondering if you can help me out with some college work. I need to do the following question:

Barium hydroxide exists in the hydrated form of Ba(OH)2.xH2O. A 0.32g sample is weighed out in a weighing boat and transferred to a crucible of known mass. The crucible is of known mass. The crucible is then heated for one minute, allowed to cool for 20 minutes and then weighed. The mass of the solid sample in the crucible is 0.20g.

Calculate the value of x in Ba(OH)2.xH2O

Please can you tell me how the hell to do this. Thanks :)

Water crystals are just another form of motion, expanding and growing in cold, melting and flowing in warmth, soaring higher and higher in the heat of the sun to cool, combine, fall, and freeze to be warmed yet again.