Design an assembly line to produce $40$ units in an $8-$hour shift. Also, find out the Idle time and line efficiency.

$\backslash$table$[[$Task$,$Immediate predecessor,Duration $($min$)],[1,-,5],[2,1,3],[3,1,7],[4,1,5],[6,3,6],[7,3,4,4],[8,2,6],[10,5,6,12]]$