A transistor is used in common-emitter mode in an amplifier circuit. When a signal of 20 mV is added to the base-emitter voltage, the base current changes by 20 μ A and the collector current changes by 2 mA. The load resistance is 5 k Ω . Calculate
(a) the factor β
(b) the input resistance Rin
(c) the transconductance
(d) the voltage gain.