A is 18 years old and B is 24 years old. What is the average age of A and B?
甲有18岁，乙有24岁，甲、乙的平均年龄是多少岁．
<gadget id="calculator">18 + 24</gadget>
<output>42</output>

<gadget id="calculator">42 / 2</gadget>
<output>21</output>

<result>21</result>