There are 15 seats in the first row of a movie theater, there are 2 more seats in each subsequent row than the front row, and 53 seats in the last row, how many rows of seats are there in this movie theater?
一个电影院的第一排有15个座位，以后每排都比前排多2个座位，最后一排有53个座位，这个电影院共有多少排座位．
<gadget id="calculator">53 - 15</gadget>
<output>38</output>

<gadget id="calculator">38 / 2</gadget>
<output>19</output>

<gadget id="calculator">19 + 1</gadget>
<output>20</output>

<result>20</result>