In an investigation of insulating materials, a student measured the temperature of a sample of water as it cooled. For one type of insulating jacket, the temperature of the water decreased from 80.0∘C80.0^\circ\text{C}80.0∘C to 55.0∘C55.0^\circ\text{C}55.0∘C. The energy transferred from the water to the surroundings was 18.9 kJ18.9\text{ kJ}18.9 kJ. The specific heat capacity of water is 4200 J/kg ∘C4200\text{ J/kg }^\circ\text{C}4200 J/kg ∘C. Calculate the mass of water used in the investigation.