The supply voltage to a room is $120\: V\: DC$. The resistance of the lead wires is $6 \Omega$. A $60\: W$ bulb is already switched on. What is the decrease of voltage across the bulb, when a $240\: W$ heater is switched on in parallel to the bulb?

Question

$\begin {array} {1 1} (A)\;0V & \quad (B)\;2.9V \\ (C)\;13.3V & \quad (D)\;10.04V \end {array}$