There are 91 people in the dance team and chorus team of Qiming School, 89 people in the chorus team and martial arts team, and 85 people in the martial arts team and musical instrument team. How many people are there in the dance team and the musical instrument team?
启铭学校舞蹈队和合唱队共有91人，合唱队和武术队共有89人，武术队和乐器队共有85人，舞蹈队和乐器队两队共有多少人？
<gadget id="calculator">85 - 89</gadget>
<output>-4</output>

<gadget id="calculator">91 + (-4)</gadget>
<output>87</output>

<result>87</result>