Sarah and Emily are planning a road trip. Sarah's car can travel 30 miles per gallon of gas, while Emily's car can travel 25 miles per gallon. They decide to travel a total distance of 600 miles and want to figure out the total amount of gas they will need and the average gas mileage for the trip if they split the driving distance equally. How many gallons of gas will each car need, and what will be their average gas mileage for the trip? Let's think step by step and output the final answer within \boxed{}.
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