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.

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【Answer】Solution: Let $n$ years later, the sum of my and my brother's ages equals my father's age at that time. Let my younger brother's current age be $x$, and my brother's age is $x+n$, we get:
$$
\begin{array}{c}
x+n+(x+n)+n=50+n \\
2 x+2 n=50 \\
x+n=25
\end{array}
$$

Answer: My brother is 25 years old this year;
Therefore, the answer is: 25.