Rush! How do I compute for heat of solution in kJ/mol given the mass, molar mass, moles, volume of water, initial temper

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Rush! How do I compute for heat of solution in kJ/mol given the
mass, molar mass, moles, volume of water, initial temperature of
water and final temperature of solution?
Example:
APPLICATION OF THE CONCEPTS IN CALORIMETRY
MgSO4
Mass of salt: 15 g
MM of salt: 120 g/mol
Moles of salt: 0.125 mol
Volume of water: 30 mL
Initial temp. of water: 28°C
Final temp. of solution: 72.8°C
Heat of solution in kJ/mol: ?
Please provide the step by step solution and explanation why was
the problem solved that way especially on the mass used in q=
mc(tf-ti). What is the reason why that X grams is used?
Thank you !