Assume that the call centre operates from $10amto6pm$ daily. There are $42$ customer representatives $in$ the call centre. Dheeraj intends $to$ measure the efficiency $of$ the call centre$s$ operations. $He$ collected the following information for analysis

$\begin{array}{cc}\text{H}\text{o}\text{u}\text{r}\text{s}& \text{N}\text{u}\text{m}\text{b}\text{e}\text{r}of\text{c}\text{a}\text{l}\text{l}\text{s}\text{s}\text{e}\text{r}\text{v}\text{e}\text{d}\\ 10am-11am& 13\\ 11am-12pm& 35\\ 12pm-1pm& 69\\ 1pm-2pm& 120\\ 2pm-3pm& 156\\ 3pm-4pm& 137\\ 4pm-5pm& 114\\ 5pm-6pm& 89\end{array}$

The table above shows the number $of$ calls that are served during $an$ hour. For example, between $10amto11am,$ a total $of13$ calls are served and completed. $Itis$ estimated that$\frac{1}{4}of$ calls are completed $in10$ minutes,$\frac{1}{3}of$ calls are completed $in15$ minutes, and the rest completed $in20$ minutes. Assume that one customer representative can only engage one call $at$ any time.

Based $on$ the above information, estimate the average number $of$ customer representatives that are busy $by$ applying Little$s$ Law. You are required $to$ explain Little$s$ Law and its three $(3)$ parameters and link the three parameters $to$ various quantities $of$ interest $in$ this question. What $is$ the average utilisation rate $of$ manpower? Show the calculation details.