Task Description Immediate Predecessors Optimistic Time $($O$)$ Most Likely Time $($M$)$ Pessimistic Time $($P$)$

A Shut down the warehouse system and remove old servers from the server room none $1$ hour $2$ hours $3$ hours

B Install new computer servers in the server room A $1$ hour $2$ hours $9$ hours

C Reconfigure warehouse terminals none $2$ hours $4$ hours $6$ hours

D Reboot the warehouse system and run diagnostics B and C $2$ hours $6$ hours $16$ hours