MCuSO₄×5H₂O = 160+90 = 250g/mol
MMgSO₄×7H₂O = 120+126 = 246g/mol
250g CuSO₄×5H₂O............90g H₂O
50g....................................x = 18g
246g MgSO₄×7H₂O.....................126g H₂O
61,5g.............................................x = 31,5g
m H₂O total = 18+31,5+200 = 249,5g