Problem $3$

A dress$-$making operation is being designed as an assembly line. The table below shows the tasks that need to be performed, their task times, and preceding tasks.

$\backslash$table$[[$Tasks$,$Description,Immedilate Predecessor,$\backslash$table$[[$Task Time$],[($in seconds$)]]],[$A$,$Cut dress body,NONE,$60],[$B$,$Cut sleeves,NONE,$90],[$C$,$Cut collar,NONE,$40],[$D$,$Sew dress body,A$,120$