Final answer:
The average speed of the reconnaissance plane is 1043.9 km/h.
Step-by-step explanation:
To find the average speed of the reconnaissance plane, we need to calculate the total distance traveled and divide it by the total time taken. The plane flies 428 km away from its base at 876 m/s, which takes approximately 0.49 hours (428 / 876 = 0.49). Then, it flies back to its base at 1314 m/s, which takes approximately 0.33 hours (428 / 1314 = 0.33). The total time taken is 0.49 + 0.33 = 0.82 hours. The total distance traveled is 428 km + 428 km = 856 km. Therefore, the average speed is 856 km / 0.82 hours = 1043.9 km/h.