Answer:
20 weeks
Explanation:
If 20 kilograms of paper have already been recycled, and the goal is 40 kilograms, subtract the 20 kg from the 40 kg. You are left with a remaining 20 kg to recycle. If the new plan has the office recycling 1 kg a week, mulitply that by 20 kg to get 20 weeks.
It will take the office 20 weeks to reach the total 40 kg of recycled paper.