11. (6 points) On Sunday morning, the older brother and the younger brother went to practice running. The older brother runs 110 meters per minute, and the younger brother runs 80 meters per minute. The younger brother ran for half an hour longer than the older brother and ended up running 900 meters more. How many meters did the older brother run?
5500
【Solution】Let's assume the older brother ran for $X$ minutes, then we have:
$$
\begin{array}{c}
(X+30) \times 80-110 X=900, \\
80 x+2400-110 x=900, \\
2400-30 x=900, \\
X=50 ; \\
110 \times 50=5500 \text { (meters); }
\end{array}
$$

Answer: The older brother ran 5500 meters.
Therefore, the answer is: 5500.