The diagram illustrates the circuit of a hair-dryer. The fan motor is rated at $0.10\,\text{kW}$ and each heater is rated at $0.40\,\text{kW}$. The price of electricity is $8.0\,\text{cents/kW h}$. How much does it cost to operate the hair-dryer for two hours when switches $P$ and $Q$ are closed and switch $R$ is open?
- A$1.6\,\text{cents}$
- B$4.0\,\text{cents}$
- C$6.4\,\text{cents}$
- D$8.0\,\text{cents}$