The cinema has 30 rows of seats, the first row has 30 seats, and each row behind has 2 more seats than the previous row. How many seats are there in this cinema?
电影院设有30排座位，第一排有30个座位，后面每一排比前一排多2个座位．这家电影院共有多少个座位？
<gadget id="calculator">30 - 1</gadget>
<output>29</output>

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

<gadget id="calculator">30 + 58</gadget>
<output>88</output>

<gadget id="calculator">30 + 88</gadget>
<output>118</output>

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

<gadget id="calculator">118 * 15</gadget>
<output>1_770</output>

<result>1_770</result>