They burned 0.2 kg of hydrogen. How much water can be heated from 0 to 100 * C?

The amount of heat during the combustion of hydrogen:
Q1 = q * mw, where q is the specific heat of combustion of hydrogen (q = 120.9 MJ / kg = 120.9 * 10 ^ 6 J / kg), mw is the mass of hydrogen (mw = 0.2 kg).
The amount of heat for heating water:
Q2 = C * m * (tк – tн), where C is the specific heat capacity of water (С = 4187 J / (kg * K)), m is the mass of water (kg), tк is the final temperature (tк = 100 ºС), tн – initial temperature (tн = 0 ºС).
Q1 = Q2 = q * mv = C * m * (tк – tн).
m = q * mw / (C (tk – tn)) = (120.9 * 10 ^ 6) * 0.2 / (4187 * (100-0)) = 57.75 kg.
Answer: You can heat 57.75 kg of water.