A power supply has an electromotive force of $120\,\text{V}$. It provides a current of $1.2\,\text{A}$ to a resistor with resistance $80\,\Omega$ and a current of $0.40\,\text{A}$ to a second resistor, as illustrated. What is the internal resistance of the power supply?
- A$15\,\Omega$
- B$20\,\Omega$
- C$60\,\Omega$
- D$75\,\Omega$