In the circuit diagram, a fixed resistor $X$ is connected in series with a battery and a variable resistor. When a current of $3.0\,\text{A}$ flows through resistor $X$, the power dissipated in it is $7.2\,\text{W}$. The variable resistor is then altered so that the power dissipated in $X$ rises by $50\%$. What is the new current in the circuit?
- A$2.4\,\text{A}$
- B$3.7\,\text{A}$
- C$4.5\,\text{A}$
- D$14\,\text{A}$