sampla mass = 42.75 g
after heating mass = 27.38 g
mass of water driven off = 42.75 -27.38
                                     Â
= 15.37 g
moles of water = 15.37 / molar mass of water
                      Â
= 15.37 / 18
                      Â
= 0.854
moles of Cu(II) sulfate = 27.38 / 159.6
                                  Â
= 0.172
by divide smallest whole number
CuSO4 = 0.172 / 0.172 = 1
H2O = 0.854 / 0.172 = 4.965 (nearly 5)
so
formula of hydrate : CuSO4 .5H2O