To find the average speed in miles per hour needed to make the 220-mile trip in 4 hours, we can use the formula:
Average speed = Total distance ÷ Time taken
Plugging in the given values, we get:
Average speed = 220 miles ÷ 4 hours
Average speed = 55 miles per hour
Therefore, Seth's family needs to maintain an average speed of 55 miles per hour to complete the 220-mile drive to their vacation spot in 4 hours.