An electric room heater works in the following repeating cycle: it operates at 1000 W for the first 20 minutes, then at 600 W for the next 40 minutes, and is switched off for 10 minutes. This cycle repeats continuously for 3 hours.
a. (i) Determine the electrical energy used in one complete cycle.
b. (ii) How many full cycles occur in 3 hours?
c. (iii) Calculate the total electrical energy consumed in 3 hours in kilowatt-hours.