6 weeks
Workers can repair 4 1/2 miles of road in two weeks. Double that to get 9 miles in four weeks. Add another 4 1/2 miles in two weeks to get 13 1/2 miles. That's a total of six weeks.
You can also just multiply 9/4 by 6:
9/4x6=54/4=13.5, or 13 1/2.
