LightEdge Technologies would like to put in place an assembly line in its Mexican facility that puts together Internet servers. The tasks needed to accomplish this, including times and predecessor relationships, are as follows:

$\backslash$table$[[$TASK$,$TIME $($MINUTES$),$IMMEDIATE PREDECESSOR$],[$A$,2\mathrm{.}9,$None$],[$B$,0\mathrm{.}2,$None$],[$C$,0\mathrm{.}25,$A$,$ B$],[$D$,0\mathrm{.}4,$A$,$ B$],[$E$,1\mathrm{.}7,$C$],[$F$,0\mathrm{.}1,$C$,$ D$],[$G$,0\mathrm{.}7,$D$],[$H$,1\mathrm{.}7,$E$,$ F$,$ G$],[$I$,1\mathrm{.}2,$H$],[$J$,2\mathrm{.}3,$I$],[$K$,2\mathrm{.}7,$I$],[$L$,1\mathrm{.}5,$J$,$ K$]]$

a$.{(}^{**})$ Draw a precedence diagram for the tasks. Suppose the takt time is $240$ seconds $($four minutes$).$ What is the theoretical minimum number of workstations?