# A pnp transistor is used in common emitter mode in an amplifier circuit. When base current is changed by an amount $\Delta I_B$, the collector current changes by 4 mA. If the current amplification factor is 60, then the value of $\Delta I_B$ is
$\begin {array} {1 1} (1)\;15\: \mu A & \quad (2)\;240\: mA \\ (3)\;66.6 \: \mu A & \quad (4)\;60 \: \mu A \end {array}$
(3) $66.6 \mu\: A$