Class 3 has 40 people, among them 28 people can ride a bicycle, 25 people can swim, 6 people can't do both sports, how many people can do both sports.
三1班有40人，其中会骑车的有28人，会游泳的有25人，两项运动都不会的有6人，两项运动都会的有多少人．
<gadget id="calculator">28 + 25</gadget>
<output>53</output>

<gadget id="calculator">40 - 6</gadget>
<output>34</output>

<gadget id="calculator">53 - 34</gadget>
<output>19</output>

<result>19</result>