To determine which distance uses the most appropriate units, let's convert all the distances to kilometers:
- \(3 \times 10^2\) kilometers = 300 kilometers
- \(3 \times 10^5\) meters:
- Convert meters to kilometers: \(3 \times 10^5 \text{ meters} \div 1000 = 3 \times 10^2\) kilometers = 300 kilometers
- \(3 \times 10^7\) centimeters:
- Convert centimeters to kilometers: \(3 \times 10^7 \text{ centimeters} \div 100,000 = 3 \times 10^2\) kilometers = 300 kilometers
- \(3 \times 10^8\) millimeters:
- Convert millimeters to kilometers: \(3 \times 10^8 \text{ millimeters} \div 1,000,000 = 3 \times 10^2\) kilometers = 300 kilometers
While all of the options represent the same distance (300 kilometers when converted), using kilometers is generally the most appropriate unit for long distances traveled in a car, making it easier to interpret.
Thus, the most appropriate unit for Janiya's road trip is \(3 \times 10^2\) kilometers.