An extension lead is being used to connect a $240\,\text{V}$ electrical supply to a heater, as illustrated. A voltmeter shows the potential difference (p.d.) across the heater is $216\,\text{V}$, and an ammeter shows that the current through the heater is $7.7\,\text{A}$. What is the total resistance of the extension lead?
- A$3.1\,\Omega$
- B$6.2\,\Omega$
- C$28\,\Omega$
- D$31\,\Omega$