it took 3.5 hours for a train to travel the distance between two cities at a velocity of 120 miles per hour. How many miles lie between the two cities?

Given:

Time: 3.5 hrs

Velocity: 120 miles/hr

Now Distance = Speed * Time

Now Velocity and speed have the same magnitude. Velocity being a vector quantity has a definite direction. Whereas speed is a scalar quantity, it indicates only the magnitude an doesn't define any direction.

Hence Distance = Velocity x time

Distance = 3.5 * 120 = 420 miles