7. (10 points) There are three locations $A$, $O$, and $B$ on a road, with $O$ between $A$ and $B$. The distance between $A$ and $O$ is 1620 meters. Two people, A and B, start from $A$ and $O$ respectively at the same time and head towards $B$. After 12 minutes, the distances of A and B from $O$ are equal; after 36 minutes, A and B meet at $B$. What is the distance between $O$ and $B$ in meters? $\qquad$ meters.
【Analysis】Suppose after 12 minutes, person A has walked $x$ meters, then A is $(1620-x)$ meters away from point $O$, so B has walked $(1620-x)$ meters. Considering that the speeds of A and B are constant, after 36 minutes, both have reached point $B$, at which time A has walked $3x$ meters, and B has walked $3 \times (1620 - x)$ meters;

Thus, $AB = 4x$, $OB = 3 \times (1620 - x)$. Given that $AO = 1620$ meters; $AB = AO + OB$, we get $3x = 1620 + 3 \times (1620 - x)$, solving for $x$ gives $x = 1080$ meters; substituting $OB = 3 \times (1620 - x) = 3 \times (1620 - 1080)$, solves the problem.

【Solution】Solution: Suppose after 12 minutes, person A has walked $x$ meters, then A is $(1620 - x)$ meters away from point $O$, so B has walked $(1620 - x)$ meters. After 36 minutes, both have reached point $B$, at which time A has walked $3x$ meters, and B has walked $3 \times (1620 - x)$ meters; since $AB = AO + OB$, we get:
$$
\begin{aligned}
3x & = 1620 + 3 \times (1620 - x), \\
6x & = 6480 \\
x & = 1080
\end{aligned}
$$
The distance between $O$ and $B$ is:
$$
3 \times (1620 - 1080) = 1620 \text{ (meters); }
$$

Answer: The distance between $O$ and $B$ is 1620 meters.
The answer is: 1620.