What you have decided to do is to go the team and asked them to give you $3$ estimates for duration for

each tasks $($pess$,$ most likely, and opt$)($given in spreadsheet$).$ From there you decided that you will

calculate the range of duration for each based on those estimates and then calculate the PERT duration

with the equation to get a sense of the variability.

So with the given critical path data $($excel spreadsheet$)$ with the $3$ estimates for each tasks duration,

using excel functionality $($no need to write VBA code$)$:

$$ Calculate the most likely duration for the critical path $/$ project.

$$ Calculate the pessimistic duration for the critical path $/$ project.

$$ Calculate the optimistic duration for the critical path $/$ project.

$$ Using the results of the most pessimistic, most likely, and most optimistic duration, using the

PERT equation to come up the PERT duration i$.$e$.=($pess $+4*$ ml $+$ opt$)/6$

$$ Calculate the range of duration values $($i$.$e$.$ the min and max$)$ that this project might take.