Use the Values in the Table to Calculate Activity Durations

Use the values in the table to calculate activity durations and variances for the project.Which path is critical? How closely should the other path be watched and why?
$$\begin{array} { | l | l | l | l | l |} \hline\text { Activity } & \text { Predecessor } & \text { Optirnistic } & \text { Likely } & \text { Pessirnistic } \\\hline \text { A } & -- & 4 & 6 & 10 \\\hline B & \text { A } & 2 & 5 & 8 \\\hline \mathrm { C} & \text { A } & 6 & 7 & 9 \\\hline \mathrm { D } & \mathrm { B } & 3 & 9 & 20 \\\hline \mathrm { E } & \mathrm { C } & 7 & 9 & 11 \\\hline \mathrm { F } & \mathrm { D } , \mathrm { E } & 7 & 11 & 19 \\\hline\end{array}$$