The circuit shown is supplied by a source with electromotive force (e.m.f.) $V$ and negligible internal resistance. A current of $3.0\,\text{A}$ flows through the $4.0\,\Omega$ resistor. What value does $V$ have?
- A$15\,\text{V}$
- B$29\,\text{V}$
- C$39\,\text{V}$
- D$51\,\text{V}$