Groups A, B, and C have 7, 8, and 5 people, respectively. In a math test, the average score of group A is 88 points, the average score of group B is 83 points, the total average score of the three groups is 85 points, what is the average score of group C?
甲、乙、丙三组的人数分别是7人、8人、5人．一次数学测验中，甲组的平均分是88分，乙组的平均分是83分，三个组的总平均分是85分，丙组的平均分是多少？
<gadget id="calculator">7 + 8 + 5</gadget>
<output>20</output>

<gadget id="calculator">85 * 20</gadget>
<output>1_700</output>

<gadget id="calculator">88 * 7</gadget>
<output>616</output>

<gadget id="calculator">83 * 8</gadget>
<output>664</output>

<gadget id="calculator">1_700 - 616 - 664</gadget>
<output>420</output>

<gadget id="calculator">420 / 5</gadget>
<output>84</output>

<result>84</result>