Consider the following work breakdown structure:

$\backslash$begin$\{$tabular$\}\{$ccccc$\}$

& & $\backslash$multicolumn$\{2\}\{$c$\}\{$ Time Estimates $($days$)\}\backslash \backslash$

Activity & Precedes & Optimistic & $\backslash$begin$\{$tabular$\}\{$c$\}$

Most $\backslash \backslash$

Likely

$\backslash$end$\{$tabular$\}$ & Pessimistic $\backslash \backslash$

$\backslash$cline $\{3-5\}$ Start & A$,$ B & $-$ & $-$ & $-\backslash \backslash$

A & C$,$ D & $44$ & $50$ & $56\backslash \backslash$

B & D & $45$ & $60$ & $75\backslash \backslash$

C & E & $42$ & $45$ & $48\backslash \backslash$

D & F & $31$ & $40$ & $49\backslash \backslash$

E & F & $27$ & $36$ & $39\backslash \backslash$

F & End & $58$ & $70$ & $82$

$\backslash$end$\{$tabular$\}$

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