Explanation:

- The speed of the train is constant. It crosses the 1000-meter bridge in 15 seconds. To find the speed of the train, use the formula: speed = distance/time = 1000 meters / 15 seconds = 66.67 meters/second.

- The train also crosses a 1300-meter bridge in 19 seconds. By the same formula, the speed is 1300 meters / 19 seconds = 68.42 meters/second.

- Equating these two equations, 66.67 meters/second = 68.42 meters/second. This method can be inaccurate due to rounding errors.

- We solve using both conditions, assuming train length = x:

- (1000 + x) / 15 = (1300 + x) / 19.

- Solving this equation will show x = 200 meters.

- Correct Answer: Option: 4, 200 meters.