Fangfang wants to buy 8 color pens of 9 yuan, and pays her aunt 100 yuan, how much should she get back.
芳芳要买8枝9元的彩笔，付给阿姨100元，应找回多少元．
<gadget id="calculator">9 * 8</gadget>
<output>72</output>

<gadget id="calculator">100 - 72</gadget>
<output>28</output>

<result>28</result>