The questions no 31 and questions 27 below are from www.oliverlehmann.com 75 free questions. pls can someone , anyone explain how they arrived at their answers. Thanks so much

(Question 31) Activity 1 has a duration of 20 days, activity 2 of 10 days, activity 3 of 5 days and activity 4 of 6 days.

What is the minimum total duration between the milestones A and B?

36 days
37 days
39 days
42 days

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