Three years ago, the father's age was exactly 6 times the age of his son Xiaogang. Now the sum of father and son's age is 55 years old. How old is Xiaogang this year?
三年前爸爸的年龄正好是儿子小刚年龄的6倍，现在父子年龄和是55岁，小刚今年多少岁．
<gadget id="calculator">55 - 3 - 3</gadget>
<output>49</output>

<gadget id="calculator">6 + 1</gadget>
<output>7</output>

<gadget id="calculator">49 / 7</gadget>
<output>7</output>

<gadget id="calculator">7 + 3</gadget>
<output>10</output>

<result>10</result>