The average age of A, B, and C is 24 years old. After joining D, the average age of the four is 25. What is the age of D?
甲、乙、丙的平均年龄是24岁，加入丁以后四人的平均年龄为25岁，则丁的年龄是多少岁．
<gadget id="calculator">25 * 4</gadget>
<output>100</output>

<gadget id="calculator">24 * 3</gadget>
<output>72</output>

<gadget id="calculator">100 - 72</gadget>
<output>28</output>

<result>28</result>