you are trying to determine the formula of your hydrate by mass difference....
OK so you have 2.000 g of this material with unknown formula (at the moment) because it has not yet been dried..
You are drying it to determine the formual by weight difference,
So you have 2,000 g and your final mass after drying is 1.565 g....the difference in the two values is the amount of water lost to drying in grams...
2.000 g - 1.565 g = 0.435 g
0.435 g is the mass of the water lost to drying
Can you figure out what to do next??