There are 30 rows of seats in the cinema, and the last row has 2 more seats than the previous row. There are 90 seats in the last row. How many seats are there in this movie theater?
电影院有30排座位，后一排都比前一排多2个座位．最后一排有90个座位，问这个电影院一共有多少个座位？
<gadget id="calculator">30 - 1</gadget>
<output>29</output>

<gadget id="calculator">2 * 29</gadget>
<output>58</output>

<gadget id="calculator">90 - 58</gadget>
<output>32</output>

<gadget id="calculator">90 + 32</gadget>
<output>122</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">122 * 15</gadget>
<output>1_830</output>

<result>1_830</result>