$1.$ Consider the following process, with a daily customer arrival rate of $140.$ Each customer gos through registration in step $1.$ There is a buffer before entering step $2,$ and the average duration of waiting in that buffer is $5$ minutes.

At step $2,$ there is a assessment to specify where each customer must go next, and depending on the findings of that assessment, usually $60\%$ of them are directed to step $3,$ which takes $10$ minutes in average for each of them, while the rest of the customers are directed to step $4$ which takes $15$ minutes in average. Once each customer goes through the respective step $(3$ or $4),$ they exit this process. Please answer the following questions accordingly.

Note:

$1)$ Consider each day as $8$ hours.

$2)$ Start and end points as well as decision points$($assessment$)$ have zero duration.

$1-1.$ What is the flow unit in this process?

$1-2.$ How much is the flow time for the buffer? $(3$ points$)$

$1-3.$ If the working hours woub be $7$ hours each day, what is the hourly rate of customer arrivals to this process? $(2$ points$)$

$1-4.$ If there are $2$ customers waiting for,or are being served at step $1$ at any point in time, what is the average time that step $1$ is taking from the beginning to the end? $(3$ points$)$

$1-5.$ As you know, only some of the customers go through step $3$ or $4,$ and the total duration of this process will be different for each stream. Knowing this, what is the process flow time? $(5$ points$)$