$\backslash$table$[[$Activity$,$Precedes,$\backslash$table$[[$Time$],[$Estima$],[$tes$],[($days$)]]],[$Optimistic$,$Most Likely,Pessimistic$],[$Start$,$A$,-,-,-],[$A$,$B$,$ C$,49,49,61],[$B$,$D$,80,95,98],[C,$E$,91,100,115],[$D$,$F$,37,39,49],[$E$,$End,$42,48,66],[F,$End,$62,65,80]]$

What is the standard deviation of path A$-$B$-$D$-$F$?$

$9\mathrm{.}06$ days

$6\mathrm{.}40$ days

$6\mathrm{.}16$ days

$7\mathrm{.}55$ days

$7\mathrm{.}07$ days