The average number of A and B is 85, and the average number of A, B, and C is 79, so what is the number of C?
甲、乙的平均数是85，甲、乙、丙的平均数是79，那么丙数是多少．
<gadget id="calculator">79 * 3</gadget>
<output>237</output>

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

<gadget id="calculator">237 - 170</gadget>
<output>67</output>

<result>67</result>