There are 48 people in a class. The head teacher asked at the class meeting: "Who has completed the Chinese homework? Please raise your hand!" 37 people raised their hands, and then asked: "Who has completed the math homework? Please raise your hand!" 42 people raised their hands , and finally asked: "Who hasn't finished their Chinese and math homework?" No one raised their hands, asking for the number of people in this class who have completed their Chinese and math homework.
一个班有48个人，班主任在班会上问："谁完成了语文作业？请举手！"有37人举手，又问："谁完成了数学作业？请举手!"有42人举手，最后问："谁语文、数学作业都没有完成？"没有人举手，求这个班语文、数学作业都完成的人数．
<gadget id="calculator">42 - 48</gadget>
<output>-6</output>

<gadget id="calculator">37 + (-6)</gadget>
<output>31</output>

<result>31</result>