y using ES, EF, LF, LS, find the slack of each activity and the critical path

Consider the following table:
ACTIVITY PREC. ACT. TIME ESTIMATES (days)
to tml tp te
A — 6 6 6
B A 4 5 6
C A 2 4 6
D B 4 6 8
E C 2 4 6
F D 1 5 3
1) Construct a PERT network.
[NOTE: This is the most crucial part of the exercise. Make sure you have the correct network
before proceeding to the next sections.]

2) By using ES, EF, LF, LS, find the slack of each activity and the critical path.

3) Find the completion time and the standard deviation (σ) for the project— round off the standard deviation to the nearest hundredth: two decimal places.

4) What is the completion time at 99.7 % confidence level?

5) What is the likelihood of this project being completed earlier than 20 days?

6) Between 19 and 22 days?