Grandpa is 80 years old this year, and his three grandsons are 30, 25, and 17 years old. How many years will it take for grandpa's age to be equal to the sum of the ages of his grandchildren?
爷爷今年80岁，他的三个孙子分别是30、25、17岁，要经过几年后爷爷的岁数等于他的孙子们的岁数之和？
<gadget id="calculator">30 + 25 + 17</gadget>
<output>72</output>

<gadget id="calculator">80 - 72</gadget>
<output>8</output>

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

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

<result>4</result>