Mr. Li opened a new phone card on the 1st of this month, and saved 100 yuan for calls. By the end of the 21st, the balance of the inquiry was 20.83 yuan. How much is Mr. Li's average daily call fee?
李老师本月1日新办了一张电话卡，存话费100元，到21日结束，查询余额显示为20.83元，李老师平均每天用话费多少元．
<gadget id="calculator">100 - 20.83</gadget>
<output>79.17</output>

<gadget id="calculator">79.17 / 21</gadget>
<output>3.77</output>

<result>3.77</result>