This year, the sum of the ages of the "father and son" is 70 years old. Seven years later, the age of the father will be twice that of the son. How old is the father this year?
今年"父子"两人年龄之和是70岁，7年后爸爸的年龄是儿子的2倍，爸爸今年多少岁？
<gadget id="calculator">7 * 2</gadget>
<output>14</output>

<gadget id="calculator">70 + 14</gadget>
<output>84</output>

<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<gadget id="calculator">84 / 3</gadget>
<output>28</output>

<gadget id="calculator">28 - 7</gadget>
<output>21</output>

<gadget id="calculator">70 - 21</gadget>
<output>49</output>

<result>49</result>