Answer:
Diane needs to travel a total of 180 miles for the round trip. Her car gets 19 miles per gallon. To find out how many gallons of gas she needs:
1. Calculate the total distance: 2 times 90 miles = 180 miles.
2. Divide the total distance by her car's miles per gallon: 180 div 19 approx 9.47 gallons.
So, Diane should make sure she has at least 10 gallons of gas for her round trip.