Answer:
cost of running the furnace during January is $5619.62
Explanation:
given data 
runs a day = 13 hours
January days = 31 days
resistance = 7.2 ohm
current = 16.7 A
cost of electricity = $0.10/kWh
to find out 
cost of running the furnace during January
solution
first we get her power consumed by furnace that is 
Power consumed = 
  ........1
put here value we get 
Power consumed = 
Power consumed = 38.7347 W
and 
Power consumed by furnace in one hour is
Power consumed by furnace in one hour is = Power consumed × 3600 
Power consumed by furnace in one hour is = 38.7347 × 3600  
Power consumed by furnace in one hour is 139.445kWh
and
Power consumed by furnace in the month of January is 
Power consumed by furnace in the month of January = 139.445kWh × 13 hours × 31 days 
Power consumed by furnace in the month of January = 56196.335 kWh
so
cost of running the furnace during January is = $0.10/kWh × 56196.335 kWh
cost of running the furnace during January is $5619.62