4. (7 points) On the athletics field, three people, A, B, and C, are running an 800-meter race on a 400-meter circular track. When A completes 1 lap, B runs $\frac{1}{7}$ lap more than A, and C runs $\frac{1}{7}$ lap less than A. If they each maintain a constant running speed, then when B reaches the finish line, C is still $\qquad$ meters away from the finish line.
【Answer】Solution: The speeds of the three people remain constant. When A runs 7 parts, B runs $7+1=8$ parts, and C runs $7-1=6$ parts; when B reaches the finish line, having run 800 meters, A has run 700 meters, and C has run 600 meters;
$$
800-600=200 \text { (meters); }
$$

Therefore, the answer is 200 .