The school carries out "I can do it" club activities. The number of people who signed up for the "Junior Table Tennis Player" is twice that of the "Campus NBA". It is known that the number of "Junior Table Tennis Players" is 21 more than that of the "Campus NBA". How many people signed up for the "Teen Table Tennis Player"?
学校开展"我能行"俱乐部活动．报名参加"乒坛小将"的人数是"校园NBA"的2倍，已知"乒坛小将"的人数比"校园NBA"多21人．报名参加"乒坛小将"的有多少人．
<gadget id="calculator">2 - 1</gadget>
<output>1</output>

<gadget id="calculator">21 / 1</gadget>
<output>21</output>

<gadget id="calculator">21 * 2</gadget>
<output>42</output>

<result>42</result>