There are 20 rows of seats in the No. 1 auditorium of a theater, and 42 seats in the seventh row. Starting from the second row, the rear row always has 2 more seats than the front row. Find the total number of seats in this auditorium.
某影院一号播放厅有20排座位，第七排有42个座位，从第二排起后面一排总比前一排多2个座位，求这个播放厅的座位总数．
<gadget id="calculator">19 * 2</gadget>
<output>38</output>

<gadget id="calculator">68 - 38</gadget>
<output>30</output>

<gadget id="calculator">20 - 7</gadget>
<output>13</output>

<gadget id="calculator">13 * 2</gadget>
<output>26</output>

<gadget id="calculator">42 + 26</gadget>
<output>68</output>

<gadget id="calculator">30 + 68</gadget>
<output>98</output>

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">98 * 10</gadget>
<output>980</output>

<result>980</result>