The energy transferred from the water in the kettle to its surroundings in 2 hours is 46 200 J. The mass of water in the kettle is 0.50 kg. The specific heat capacity of water is 4200 J/kg °C. What is its temperature after 2 hours?

The water loses 4200 J/kg °C * 0.5 kg = 2100 J/°C

As it's lost 46,200 J in total (regardless of the time it took for this to happen), it must have reduced in temperature by 46,200 J   /   2100 J/°C    =    22°C.

Assuming 100°C initially, temperature of water in kettle is now 78°C.