D E for chemical processes, since little or no work is usually done in solution chemistry.
Calorimetry is the science of measuring heat.
D E. Heat is a measure of energy transferred between objects of different temperatures. D T where m is the mass of substance and C sp is the specific heat of the substance. Heat capacity of water is assumed to be exact for this problem. Thus the answer will have only three sig figs since two sig figs for 750 since using multiplication, but tenths place for addition of 7.5 to 20.00. In fact a slight error is introduced in this calculation because heat capacity changes slightly with temperature.