Final answer:
Emma kept track of the gallons of gas used on her business trips to monitor her car's fuel efficiency.
Step-by-step explanation:
Emma kept track of the gallons of gas used on her business trips b) To monitor her car's fuel efficiency. By keeping track of how many gallons of gas she used on each trip, she can calculate her car's fuel efficiency by dividing the distance traveled by the number of gallons used. This will help her assess the performance of her car and make informed decisions regarding her fuel consumption.