Hi, I've been attempting this problem all week now and I can't seem to even begin to obtain an answer which is highly frustrating, so here's the problem: An electric boiler is required to raise the temperature of 90 litres of water per hour by 35oC. If the input required to affect this change is 4.3235kW, calculate the efficiency of the boiler. Find the cost of operating the boiler for a period of 5 hours if electrical energy costs 13p/kWhr. 2. Relevant equations I have some equations which could be useful, but I can't seem to apply them to this particular problem, the equations I have looked at are: n (efficiency) = Useful energy output/Total energy input and Maximum theoretical thermal efficiency = (Temperature Hot - Temperature Cold)/Temperature Hot Unfortunately I have no attempted solution to show as I haven't been able to get anywhere with this. I do know however that the temperature will have to be converted into Kelvin (the easy bit). I have thought about considering the Specific Heat Capacity of water but don't know how it would apply to this problem. Any help is greatly appriciated.