The following table contains information concerning four jobs that are awaiting processing at a work center.

$\backslash$table$[[$Job$,\backslash$table$[[$Job Time$],[($days$)]],\backslash$table$[[$Due date$],[($days$)]]],[$A$,14,20],[$B$,10,16],[$C$,7,15],[$D$,6,17]]$

Determine the average flow time using the SPT rule.

Select the correct response:

$21\mathrm{.}75$

$21$

$26\mathrm{.}5$

$19\mathrm{.}75$