There are three numbers, the average of A and B is 81, the average of A and C is 85, and the average of B and C is 86. What is the average of the three numbers A, B, and C?
有三个数，甲数和乙数的平均数是81，甲数和丙数的平均数是85，乙数和丙数的平均数是86．甲、乙、丙三个数的平均数是多少．
<gadget id="calculator">81 * 2</gadget>
<output>162</output>

<gadget id="calculator">85 * 2</gadget>
<output>170</output>

<gadget id="calculator">86 * 2</gadget>
<output>172</output>

<gadget id="calculator">162 + 170 + 172</gadget>
<output>504</output>

<gadget id="calculator">504 / 2</gadget>
<output>252</output>

<gadget id="calculator">252 / 3</gadget>
<output>84</output>

<result>84</result>