The average age of A and B is 30 years old, and the average age of A, B, and C is 29 years old. What is the age of C?
甲乙两人平均年龄是30岁，甲乙丙三人的平均年龄是29岁，丙的年龄是多少
<gadget id="calculator">29 * 3</gadget>
<output>87</output>

<gadget id="calculator">30 * 2</gadget>
<output>60</output>

<gadget id="calculator">87 - 60</gadget>
<output>27</output>

<result>27</result>