Physics question?

My first answer would be check your units..teachers like mixing them up. If you already tried that, water has a heat capacity of 4180 J/kgK so find out how much you have in the barrel. A Watt is 1J/s ( kW is 10x3 ) so the quanity of energy in your barrel devided by 10x3 would give you your time in second. Convert in hours after. Try writting those equation on a piece of paper, it help.