It took Xiaodong 3 weeks to write 420 big characters. How many big characters does he write on average every day?
小东用了3个星期写了420个大字，他平均每天写多少个大字？
<gadget id="calculator">3 * 7</gadget>
<output>21</output>

<gadget id="calculator">420 / 21</gadget>
<output>20</output>

<result>20</result>