There are 30 rows of seats in the auditorium, and each row has the same number of seats. Xiaohua sits in the seventh row. Counting from the beginning of the row, he is the sixth, and counting from the end of the row, he is the 13th. How many seats can there be in the auditorium? classmate?
礼堂有30排座位，每排座位同样多，小华坐在第七排，从排头开始数，他是第六个，从排尾数起，他是第13个，大礼堂里共能坐多少个同学？
<gadget id="calculator">13 - 1</gadget>
<output>12</output>

<gadget id="calculator">6 + 12</gadget>
<output>18</output>

<gadget id="calculator">18 * 30</gadget>
<output>540</output>

<result>540</result>