Castel's average speed from the science museum to mountains is 20 km/h
Let x represent Castel' average speed.
Sumalee left one hour later and caught up with Castel after two hours, Let us assume the distance covered is d:
For Castel:
For Sumalee:
3x = 2x + 20
x = 20 km/h
Therefore Castel's average speed from the science museum to mountains is 20 km/h
Find out more on average speed at: https://brainly.com/question/4931057