The line graph shows the Import and Export values (in million USD) of a country over 5 years. Year 2018: Imports 400, Exports 300. Year 2019: Imports 450, Exports 350. Year 2020: Imports 500, Exports 480. Year 2021: Imports 550, Exports 400. Year 2022: Imports 600, Exports 550. In which year was the difference between Imports and Exports the highest?