9. (5 points) When Dad was celebrating his 50th birthday, the younger brother said: “When I grow up to be as old as my brother is now, the sum of our ages at that time will be exactly equal to Dad's age then.” So, the brother is $\qquad$ years old now.

将上面的文本翻译成英文，请保留源文本的换行和格式，直接输出翻译结果。