There are 48 people in Class A. The teacher asked in the class: "Who has finished the Chinese homework? Please raise your hand!" 37 people raised their hands, and then asked: "Who has finished the math homework? Please raise their hands!" 42 people raised their hands ． Finally, I asked: "Who hasn't finished their Chinese and math homework?" No one raised their hands. Find the number of people who have completed both Chinese and mathematics homework in this class.
甲班有48人，老师在班上问："谁做完了语文作业？请举手！"有37人举手，又问："谁做完了数学作业？请举手！"有42人举手．最后问："谁语文、数学作业都没有做完？"没人举手．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>