Xiaoming's father's salary in September is 2100 yuan. According to the regulations, the part exceeding 1600 yuan must pay personal income tax at 5%. How much personal income tax should Xiaoming's father pay in September?
小明爸爸九月份工资2100元，按规定超过1600元的部分必须按5%缴纳个人所得税．小明爸爸九月份应交纳个人所得税多少元？
<gadget id="calculator">2_100 - 1_600</gadget>
<output>500</output>

<gadget id="calculator">5 / 100</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">500 * (1/20)</gadget>
<output>25</output>

<result>25</result>