Final answer:
Seth should use the equation t = d / v, where t is the time in hours, d is the distance, and v is the velocity or speed of the train.
Step-by-step explanation:
To write an equation that shows how many hours a trip takes in terms of the trip's distance, Seth should use the formula:
t = d / v
where t is the time in hours, d is the distance, and v is the velocity or speed of the train. In this case, the velocity of the train is given as 220 kilometers per hour.