Time Estimates $($in weeks$)$ for SOM's Bus Project is given in the following table.

$\backslash$table$[[$Activity$,$Optimistic time,Most likely time,Pessimistic time$],[$A$,2,4,6],[$B$,3,5,8],[$C$,4,6,8],[$D$,4,6,9]]$

Please help the project management team to find the standard deviation of Activity D$.$

keep two decimals if not exact, either round up or down is ok$.$ For example, for or $\mathrm{.}13)$ and or $\mathrm{.}14$