There are 42 students in Class 3 and 5, 21 students can play chess, 17 students can play Go, and 10 students can neither. How many players can play both kinds of chess?
三5班有42名同学，会下象棋的有21名同学，会下围棋的有17名，两种棋都不会的有10名．两种棋都会下的有多少名．
<gadget id="calculator">10 - 42</gadget>
<output>-32</output>

<gadget id="calculator">21 + 17 + (-32)</gadget>
<output>6</output>

<result>6</result>