Question

Mileposts mark distance along a highway. A car traveled from milepost 15 to milepost 185. To calculate the average speed of the car, what additional information is necessary? the minimum and maximum speeds of the car the initial and final speeds of the car the time of the journey the total length of the highway

Answer 1

Speed = (distance covered) / (time to cover the distance).

You know the distance covered ...  Sign 15 to sign 185 = 170 miles .

Now, to calculate the car's average speed, you need to know
how long it took him to cover the distance. 

That's "the time of the journey".