AS Chemistry Revision Question Difficulty: please help

I am usually ok at answering these questions, but this one is different as it is asking me to find the enthalpy change per mole of the element/compound in the solution rather than the one being added, and it is really confusing me.

The question: Addition of 1.6g of Magnesium to 100cm3 of 2M copper sulphate solution raised the temperature by 45'C. Find the enthalpy change per mole of copper sulphate in the reaction.

I would really appreciate some help on this. Kind regards 👍🏻

moles of Mg = mass/Ar
moles of copper sulfate = molarity x volume

which ever is the smaller is the limiting reagent

E = mcΔT

energy per mol = energy/moles of limiting reagent

Thank you, I was dividing the mass 100 by the Ar 95.6, then divided the energy 18810 by the former figure, getting the wrong answer.

Could I just ask you to explain why it's different working for finding the moles of Mg and CuS?