By plane, each passenger can carry 20 kilograms of luggage free of charge. If it exceeds 20 kilograms, the baggage fee shall be paid according to 1.5% of the original price of the air ticket for each kilogram of the excess part. Teacher Li flew from Zhengzhou to Beijing, and the air ticket was 420 yuan after a 30% discount. He brought 30 kilograms of luggage, how much is the luggage fee.
乘坐飞机，每位旅客可以免费携带20千克行李．如果超过20千克，超过的部分每千克需按飞机票原价的1.5%付行李费．李老师从郑州乘飞机到北京，飞机票打七折后是420元．他带了30千克的行李，应付行李费多少元．
<gadget id="calculator">70 / 100</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">420 / (7/10)</gadget>
<output>600</output>

<gadget id="calculator">30 - 20</gadget>
<output>10</output>

<gadget id="calculator">1.5 / 100</gadget>
<output>0.015</output>

<gadget id="calculator">600 * 10 * 0.015</gadget>
<output>90</output>

<result>90</result>