The ABC company is undertaking a new project that has $4$ activities. A list of activities and their optimistic completion time, the most likely completion time, and the pessimistic completion time $($all in days$)$ for a new contract are given in the following table:a$.$ Determine the expected completion time and variance for each activity.b$.$ Determine the total project completion time and the critical path for the project.c$.$ Determine ES$,$ EF$,$ LS$,$ LF$,$ and slack for each activity.d$.$ What is the probability that the company will finish the project in $21$ days or less?ActivityambImmediate Predecessor$($s$)$A$91011-$B$3915-$C$91011$AD$5811$B