There are three numbers. It is known that the sum of A and B is 60, the sum of B and C is 42, and the sum of A and C is 54. What is the average of these three numbers.
有三个数，已知甲、乙之和是60，乙、丙之和是42，甲、丙之和是54．这三个数的平均数是多少．
<gadget id="calculator">60 + 42 + 54</gadget>
<output>156</output>

<gadget id="calculator">156 / 2 / 3</gadget>
<output>26</output>

<result>26</result>