To calculate the time it takes for an automobile to travel a certain distance at an average velocity, you can use the formula:
Time = Distance / Velocity
Given that the distance is ninety kilometers and the average velocity is thirty kilometers per hour, we can substitute these values into the formula:
Time = 90 km / 30 km/h
Dividing 90 by 30 gives us:
Time = 3 hours
Therefore, it takes 3 hours for the automobile to travel ninety kilometers at an average velocity of thirty kilometers per hour.