Uncle Wang is 70 years old. He has three grandsons, one is 20 years old, the other is 15 years old, and the other is 5 years old. May I ask how many years later, the sum of the ages of Uncle Wang and their three grandchildren will be equal?
王大爷70岁，他有三个孙子，一个20岁，一个15岁，一个5岁．请问几年后，王大爷与他们三个孙子的年龄和相等？
<gadget id="calculator">70 - 20 - 15 - 5</gadget>
<output>30</output>

<gadget id="calculator">1 - 1</gadget>
<output>0</output>

<gadget id="calculator">1 + 1 + 0</gadget>
<output>2</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<result>15</result>