Consider the following work breakdown structure:

$\backslash$table$[[,,$Time Estimates $($days$)],[$Activity$,$Precedes,Optimistic,Most Likely,Pessimistic$],[$Start$,$A$,$ B$,-,-,-],[$A$,$C$,$ D$,44,50,56],[$B$,$D$,45,60,75],[$C$,$E$,42,45,48],[$D$,$F$,31,40,49],[$E$,$F$,27,36,39],[$F$,$End,$58,70,82]]$

What is the estimated slack time for activity $D?$