The mother is 38 years old this year, and the daughter is 20 years old. When the combined age of mother and daughter is 50 years old, how many years ago?
妈妈今年是38岁，女儿是20岁，当母女俩年龄之和是50岁时，是多少年前的事．
<gadget id="calculator">38 - 20</gadget>
<output>18</output>

<gadget id="calculator">50 + 18</gadget>
<output>68</output>

<gadget id="calculator">68 / 2</gadget>
<output>34</output>

<gadget id="calculator">38 - 34</gadget>
<output>4</output>

<result>4</result>