What amount of heat is given to the environment by boiling water weighing 3 kg when it cools down to 50 °?

The amount of heat that boiling water gave to the environment:
Q = C * m * (tn – tc), where C is the specific heat capacity of water (we take C = 4200 J / (kg * K)), m is the mass of water (m = 3 kg), tn is the initial water temperature (tn = 100 ºС, since the water cooled down from the boiling water state), tк – the final water temperature (tк = 50 ºС).
Let’s calculate the heat that the boiling water has given to the environment:
Q = C * m * (tн – tк) = 4200 * 3 * (100 – 50) = 630,000 J = 0.63 MJ.
Answer: Boiling water gave 0.63 MJ of heat.