The father is 45 years old, the mother is 40 years old, and the sum of the ages of the four children is 55 years old. After a few years, the sum of the ages of the father and mother is equal to the sum of the ages of the four children?
父亲45岁，母亲40岁，四个孩子的年龄之和是55岁．问几年后，父亲母亲的年龄之和等于四个孩子年龄之和？
<gadget id="calculator">40 - 55</gadget>
<output>-15</output>

<gadget id="calculator">45 + (-15)</gadget>
<output>30</output>

<gadget id="calculator">4 - 1 - 1</gadget>
<output>2</output>

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

<result>15</result>