This year, the age difference between the grandfather and father is 6 times the age of the son, and the sum of the ages of the son and father is 30 years younger than the age of the grandfather. How old is the son this year?
今年，爷爷和爸爸的年龄差是儿子年龄的6倍，而儿子与爸爸的年龄之和比爷爷的年龄小30岁．儿子今年多少岁．
<gadget id="calculator">30 / 5</gadget>
<output>6</output>

<result>6</result>