Mr. Zhang bought two footballs. He gave the salesperson 100 yuan and got back 20 yuan. How much is each football?
张老师买两个足球，他给售货员100元，找回20元，每个足球多少钱？
<gadget id="calculator">100 - 20</gadget>
<output>80</output>

<gadget id="calculator">80 / 2</gadget>
<output>40</output>

<result>40</result>