The average age of me, my father, and my mother is 30 years old this year. It is known that the average age of my father and mother is 39 years old. How old do you think I am this year?
我、爸爸、妈妈三人今年的平均年龄是30岁，已知爸爸和妈妈两人的平均年龄是39岁，你猜我今年是多少岁？
<gadget id="calculator">30 * 3</gadget>
<output>90</output>

<gadget id="calculator">39 * 2</gadget>
<output>78</output>

<gadget id="calculator">90 - 78</gadget>
<output>12</output>

<result>12</result>