Wujin Cinema has 8 rows downstairs with a total of 420 seats. There are 9 rows upstairs with 30 seats in each row. How many fewer seats are upstairs than downstairs?
武进电影院楼下有8排，共有420个座位，楼上有9排，每排30个座位，楼上比楼下少多少个座位？
<gadget id="calculator">9 * 30</gadget>
<output>270</output>

<gadget id="calculator">420 - 270</gadget>
<output>150</output>

<result>150</result>