Fangfang is 6 years old this year, and when Fangfang turned 10, her father happened to be 39 years old. How old is dad?
芳芳今年6岁，芳芳满10岁时，爸爸正好39岁．爸爸今年多少岁？
<gadget id="calculator">10 - 6</gadget>
<output>4</output>

<gadget id="calculator">39 - 4</gadget>
<output>35</output>

<result>35</result>