A 2.5 g sample of a hydrate of Ca(NO3)2 was heated, and only 1.7 g of the anhydrous salt remained. What percentage of water was in the hydrate?

I divided 11.7/ 2.5 = 4.68 ... am i doing this right... what do i do nxt?

Also,
A 5.0 g sample of Cu(NO3)2 X nH20 is heated, and 3.9 g of the anhydrous salt remains. What is the value of n ?