A small software development project has $9$ major activities. The times are estimated and provided in the network below. $[15$ points$]$

$($a$)$ Using the method of ES$,$ EF$,$ LS$,$ and LF$,$ determine the project completion time?

$($b$)$ Find the critical path$($s$).$

$($c$)$ State the non$-$critical activities.

$($d$)$ Explain what it means if an activity has a slack of zero $($give an example$).$

$($e$)$ Explain what it means if an activity has a slack of non$-$zero $($give an example$)$