Students from Xinghua Primary School actively participated in environmental protection activities. The girls in the first class of the third grade collected 21 used batteries, and the number of used batteries collected by the boys was twice that of the girls. How many batteries did the first class of the third grade collect in total?
兴华小学的同学积极参加环保活动．三年级一班女生收集了21节废旧电池，男生收集的废旧电池数量是女生的2倍，三年级一班同学一共收集了多少节？
<gadget id="calculator">21 * 2</gadget>
<output>42</output>

<gadget id="calculator">42 + 21</gadget>
<output>63</output>

<result>63</result>