a) 3 bulbs rated 40W for 5 hrs : Â Â Â 3*40*5 = 600 Watt hours
b) A heater rated 1500W for 3hrs     3* 1500 = 4500 Watt hours
c) A fridge rated 400W Â Â Â Â Â Â Â Â Â Â Â Â Â
Would assume the Fridge would run for 24 hours a day :400*24 =  9600 Watt hours                Â
Total Watt hours for 1 day :
600 + 4500 + 9600 = 14700 Watt hours
Unit of Electricity is in kWh
14 700 wh = Â 14700/1000 = 14.7kWh
But 1kWh = Rs.3
14.7 kWh = Â Â 3*14.7 = 44.1Â
Total cost = Â Â Â Rs.44.10