From the principle of conservation of energy, heat gain should equal to the magnitude of heat lost.
Heat gained = 3974.8 J
Heat lost = 5020.8 J
Since there is a difference, that difference has got into the calorimeter.
So, heat dissipated to calorimeter = 5020.8 - 3974.8 =1046 J
Now, heat capacity is given by:
Q is the amount of energy
Theta is the change in temperature of the calorimeter.
Can you finish that now?