Lillian's office recycled a total of 12 kilograms of paper over 3 weeks. How many weeks will it take Lillian's office to recycle a total of 20 kilograms of paper? Assume the relationship is directly proportional.
If 12 kilograms of paper is recycled over a period of 3 weeks, then the rate of recycling is 12/3 = <<12/3=4>>4 kilograms of paper per week.
If the rate of recycling is 4 kilograms per week, then it will take 20/4 = <<20/4=5>>5 weeks to recycle a total of 20 kilograms of paper. Answer: \boxed{5}.