The school's aviation model group has 39 people, 3 people less than twice the number of the computer group. How many people are there in the computer group?
学校航模组有39人，比电脑组人数的2倍少3人．电脑组有多少人？
<gadget id="calculator">39 + 3</gadget>
<output>42</output>

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

<result>21</result>