student's age in 1998 is exactly equal to the sum of the digits of the year of his birth. How old was this student in 1998?
一个学生1998年的年龄正好等于他出生那一年年份的各位数字之和，这个学生1998年有几岁？
<gadget id="calculator">1_998 - 1_980</gadget>
<output>18</output>

<result>18</result>