A Network Consists of the Following List A Draw the Network Diagram

A network consists of the following list. Times are given in weeks.
$$\begin{array} { | c | c | c | c | c | } \hline \text { Activity } & \text { Preceding } & \text { Optimistic } & \text { Probable } & \text { Pessimistic } \\\hline \mathrm { A } & - - & 5 & 11 & 14 \\\hline \mathrm { B } & - & 3 & 3 & 9 \\\hline \mathrm { C } & - - & 6 & 10 & 14 \\\hline \mathrm { D } & \mathrm { A } , \mathrm { B } & 3 & 5 & 7 \\\hline \mathrm { E } & \mathrm { B } & 4 & 6 & 11 \\\hline \text { F } & \mathrm { C } & 6 & 8 & 13 \\\hline \text { G } & \mathrm { D } , \mathrm { E } & 2 & 4 & 6 \\\hline \mathrm { H } & \mathrm { F } & 3 & 3 & 9 \\\hline\end{array}$$ a. Draw the network diagram.
b. Calculate the expected duration and variance of each activity.
c. Calculate the expected duration and variance of the critical path.
d. Calculate the probability that the project will be completed in less than 28 weeks.