Answer: The actual distance is 900 miles.
Explanation:
The scale is:
1 in = 300 miles.
This means that in the map, we have that 1-inch corresponds to 300 miles, so if in the map we have that the distance from Denver to Chicago is 3 inches, this means that the real distance is 300 miles for each inch, this is equal to:
3*300 miles = 900 miles