The sum of the ages of the four people is 81 years old, the youngest is 7 years old, and the sum of his and the oldest is 11 years older than the sum of the ages of the other two. How old is the oldest?
四个人的年龄之和是81岁，最小的7岁，他和最大的年龄之和比另外两个人年龄之和大11岁，最大的年龄是多少岁？
<gadget id="calculator">81 - 11</gadget>
<output>70</output>

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

<gadget id="calculator">70 / 2</gadget>
<output>35</output>

<gadget id="calculator">11 - 7</gadget>
<output>4</output>

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

<result>39</result>