What is the speed of the spray rig in miles per hour if it takes 7.5 minutes to travel half a mile?

To determine the speed of the spray rig in miles per hour, we can start by calculating the total distance covered in an hour. Since the rig travels half a mile in 7.5 minutes, we first need to convert that time into hours:

7.5 minutes is equivalent to 7.5 ÷ 60 = 0.125 hours.

Since the rig covers half a mile in that time, we can find the speed by using the formula:

Speed = Distance / Time.

In this case, the distance is 0.5 miles, and the time is 0.125 hours. Therefore, the speed is calculated as follows:

Speed = 0.5 miles / 0.125 hours = 4 miles per hour.

This calculation shows that the correct answer is indeed 4 mph, as it accurately reflects the relationship between distance and time at which the spray rig is traveling.