The grandfather is 70 years old this year, and the sum of the ages of the three grandsons is 40 years old. How many years later, the sum of the ages of the three grandchildren will be equal to the age of the grandfather.
爷爷今年70岁，三个孙子的年龄和是40岁，多少年后，三个孙子的年龄和与爷爷的年龄相等．
<gadget id="calculator">70 - 40</gadget>
<output>30</output>

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

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

<result>15</result>