There are 96 students in Class A and Class B, 89 students in Class B and Class C, and 86 students in Class C and Class D. How many people are there in Class A and Class D?
甲班和乙班共96人，乙班和丙班89人，丙班和丁班共86人，问甲班和丁班共多少人．
<gadget id="calculator">86 - 89</gadget>
<output>-3</output>

<gadget id="calculator">96 + (-3)</gadget>
<output>93</output>

<result>93</result>