Three recent university graduates have formed a partnership and have opened an advertising firm. Their first project consists of activities listed in the following table. Refer: Normal Probability Table. $($Round the final answers to $4$ decimal places.$)$

Time in Days

Activity Immediate

Predecessor$($s$)$ Optimistic Most Likely Pessimistic

A $567$

B $8811$

C A $6811$

D $91215$

E C $569$

F D $567$

G F $237$

H B $445$

I H $578$

END E$,$ G$,$ I

a$.$ This part of the question is not part of your Connect assignment.

b$.$ What is the probability that the project can be completed in $24$ days or less? In $21$ days or less?