A movie theater has two floors, each floor has the same seats, and there are several rows of seats, the first row has 20 seats, each subsequent row has 3 seats more than the previous row, and the last row has 53 seats, how many seats does this movie theater have? seats.
某电影院有两层，每层的座位一样，都有若干排座位，第一排20个座位，以后每一排比前一排多3个座位，最后一排有53个座位，这个电影院一共有多少个座位．
<gadget id="calculator">20 + 53</gadget>
<output>73</output>

<gadget id="calculator">53 - 20</gadget>
<output>33</output>

<gadget id="calculator">33 / 3</gadget>
<output>11</output>

<gadget id="calculator">11 + 1</gadget>
<output>12</output>

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">73 * 6</gadget>
<output>438</output>

<gadget id="calculator">438 * 2</gadget>
<output>876</output>

<result>876</result>