A calorimeter contains 30.0 mL of water at 12.0 C. When 1.60 g of X (a substance with a molar mass of 45.0 g/mol) is added, it dissolves via the reaction

X (s) + H2O (l) → X (aq)
and the temperature of the solution increases to 28.5 C.

Calculate the enthalpy change, Delta H, for this reaction per mole of X.

Assume that the specific heat and density of the resulting solution are equal to those of water 4.18 J/(g C and 1.00 g/mL and that no heat is lost to the calorimeter itself, nor to the surroundings.

I'm not sure which equation to use. I tried q=mcdT and I got 3.10365 but that was wrong

You have to find out the enthalpy change of the water first so 30 x 4.18 x 16.5. Then you take the negative value of that to be you enthalpy change for the mass of X. Next you find the moles of X that are present by dividing the mass of X present by it's molar mass. Lastly you take the enthalpy for the dissolved X (the enthalpy for the amount) then divide that by the number of moles of X you have.