12. How much work will a 4.0 HP (3 kW) motor do in half an hour? Show all work. 13. A 1500 W kettle warms 1.00 kg of water from 18C to 88C in a time of 3.6 min. How efficient is the kettle? 14. One difficulty that HVAC (Heating Ventilating and Air-Conditioning) technicians have when replacing a furnace for a customer is that the customer often feels that the technicians are \"ripping them off\" by giving them much smaller furnace than they originally had. a. The old furnace is 60% efficient and is sized at 180000 btu (don't worry too much about the units). How much energy (in btu) was heating the house before the exchange. b. The new furnace is 92% efficient. What size of furnace is needed to produce the same heat energy to the house (in btu)