The reading room of a bilingual elementary school is open one day. At the beginning, each person has one seat, and it happens to be full. The students leave 5%, and 21 people come in. At this time, there are not enough seats. There are 12 people with one seat for two people. How many seats are there in the school reading room? seat?
双语小学某天阅览室开放，开始每人一个座位，正好坐满，学生走了5%，又进来21人，这时座位不够，有12人每两人一个座位，学校阅览室一共有多少个座位？
<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">21 - 6</gadget>
<output>15</output>

<gadget id="calculator">5 / 100</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">15 / (1/20)</gadget>
<output>300</output>

<result>300</result>