Grandpa Wang is 80 years old this year. He has three grandchildren: the eldest grandson is 30 years old, the second grandson is 25 years old, and the youngest grandson is 17 years old. How many years later, the age of Grandpa Wang will be exactly equal to the sum of the ages of his three grandsons?
王爷爷今年80岁．他有三个孙子：大孙子今年30岁，二孙子今年25岁，小孙子今年17岁，几年以后王爷爷的岁数正好等于他三个孙子的年龄和？
<gadget id="calculator">80 - 30 - 25 - 17</gadget>
<output>8</output>

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

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

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<result>4</result>