Dad is 45 years old this year. He has three sons. The eldest son is 15 years old, the second son is 11 years old, and the third son is 7 years old.
爸爸今年45岁，他有三个儿子，大儿子15岁，二儿子11岁，三儿子7岁，要经过几年后爸爸的岁数等于他的儿子们岁数的和？
<gadget id="calculator">45 - 15 - 11 - 7</gadget>
<output>12</output>

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

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

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<result>6</result>