Oliver 31/75Q : Kindly Explain

Hi Kindly explain 31 question from Oliver 75 online question


 

ES of Activity1 =1 EF of Activity1 =20

ES of Activity 2 =21 EF of Activity2 =30

EF of Activity3 =28 ( Since Activity2 and Activity3 are having FF-2 relationship i.e Activity3 will finish 2 days before Activity2 finishes)

ES of Activity4 =32 as there is 3 days lag after Activity3

EF of Activity4 = 37