First use the mass of the copper sulfate after all the water is gone to determine the moles of CuSO4
0.89/159.5 = 0.0055
The mass loss on heating can be used to determine the moles of water lost:
(1.39 - 0.89)/[(2 x 1) + 16] = 0.0278
Now determine the ratio of water to CuSO4
0.0278/0.0055 ~ 5
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(because its moles of water to moles of copper sulfate ratio)