Answer: 856.59 km/h
Explanation:
Length of a planet's orbit around a star = 17,680,000 km.
Days to complete full orbit = 860 days
Number of hours to complete full orbit = 860 × 24 hours = 20640 hours
The planets average speed in km/h will be:
= Distance / Time
= 17,680,000 / 20640
= 856.59 km/h
Note: 24 hours = 1 day