Above table shows recent project completion times $($days$)$ along with their difficulty level. The difficulty levels are indicated by A$,$ Band C with the level of difficulty increasing in the same order of the alphabets.

a$)$ Construct an appropriate control chart. $5$ M

b$)$ Is the process under control? If not, what are the special causes? If the process is not under control, what are the revised control limits$?2$ M

c$)$ What are the $\backslash (1\backslash$sigma $\backslash )$ and $\backslash (2\backslash$sigma $\backslash )$ control limits for the process? $3$ M

d$)$ Is there any trend or clustering or any other phenomenon that can be observed in the control chart? $2$ M