A transistor is used in common-emitter mode in an amplifier circuit. When a signal of 10 mV is added to the base-emitter voltage, the base current changes by $10 \mu \mathrm{~A}$ and the collector current changes by 1.5 mA . The load resistance is $5 \mathrm{k} \Omega$. The voltage gain of the transistor will be $\_\_\_\_$