Xiaoli: I bought 4 small footballs; salesperson aunt: I will charge you 100 yuan, and I will find you 28 yuan; how much is each small football on average?
小力：我买4个小足球；营业员阿姨：收你100元，找你28元；平均每个小足球多少元？
<gadget id="calculator">100 - 28</gadget>
<output>72</output>

<gadget id="calculator">72 / 4</gadget>
<output>18</output>

<result>18</result>