Teacher Li's monthly income is 4,000 yuan. According to regulations, the part of the income exceeding 3,500 yuan is subject to personal income tax at 3%. How much personal income tax should Mr. Li pay?
李老师月收入4000元，按规定，收入超过3500元的部分，要按3%征收个人所得税．李老师应缴纳个人所得税多少元？
<gadget id="calculator">4_000 - 3_500</gadget>
<output>500</output>

<gadget id="calculator">3 / 100</gadget>
<output>3/100 = around 0.03</output>

<gadget id="calculator">500 * (3/100)</gadget>
<output>15</output>

<result>15</result>