The diagram shows a circuit that includes two resistors, P and Q, together with a power supply whose internal resistance is negligible. The current through resistor P is $2.0\,\text{A}$, and resistor P dissipates $18\,\text{W}$ of power. Resistor Q loses $240\,\text{J}$ of energy when a charge of $40\,\text{C}$ flows through it. What is the electromotive force (e.m.f.) of the power supply?
- A$3.0\,\text{V}$
- B$6.0\,\text{V}$
- C$9.0\,\text{V}$
- D$15\,\text{V}$