When rounding to the nearest ten, what is the least whole number that rounds to 310? What is the greatest whole number that rounds to 310?

Every weekday, mr. jones bikes from his home to his job. sometimes he rides along two roads, the long route that is shown by the solid lines. other times, he takes the shortcut shown by the dashed line. how many fewer kilometers does mr. jones bike when he takes the shortcut instead of the long route?