The average of the three numbers A, B, and C is 85, the average of the two numbers A, B, and B is 87, and the average of the two numbers B, C is 78. What is the B number?
甲乙丙三个数的平均数是85，甲乙两数的平均数是87，乙丙两数的平均数是78．乙数是多少？
<gadget id="calculator">87 * 2</gadget>
<output>174</output>

<gadget id="calculator">78 * 2</gadget>
<output>156</output>

<gadget id="calculator">174 + 156</gadget>
<output>330</output>

<gadget id="calculator">85 * 3</gadget>
<output>255</output>

<gadget id="calculator">330 - 255</gadget>
<output>75</output>

<result>75</result>