Answer:
70 km/hr
Step-by-step explanation:
Distance between town A and B = 210 km
Della's speed = 60 km/hr
Time taken by Della = distance / speed
Time taken by Della = 210 km / 60km/ hr
Time taken by Della = 3.5 hours
Since Nick left half an hour later Than Della ;
Then, Nick's travel time = 3.5 - 0.5 = 3 hours
Nick's average speed = Distance /time
Nick's average speed = 210 / 3 = 70km/hr