A TV station broadcasts a TV series and has broadcast 21 episodes. The ratio of the number of episodes that have been broadcast to the number of episodes that have not been broadcast is 3:5. How many episodes did not air?
某电视台播放一部电视剧，已经播了21集，已经播的和未播的集数比是3：5．没有播的有多少集？
<gadget id="calculator">5 / 3</gadget>
<output>5/3 = around 1.666667</output>

<gadget id="calculator">21 * (5/3)</gadget>
<output>35</output>

<result>35</result>