How to find out..

[Palooza]

Well I've been given a scenario, and cannot work out what i have to do to work ot the answer, so im wondering if any of you know how to.

Below is the brief

CheapShops is a supermarket. The supermarket has twenty checkouts. CheapShops has just launched
a marketing campaign that guarantees that no more than four people will be in a queue for any
checkout at any time. In order to achieve this, the supermarket will need to have sufficient till-trained
staff available during each shift.
The shop is open for sixteen hours a day and is staffed by two separate eight hour shifts.
The owners of the supermarket want to be able to plan how many till-trained staff are needed for each
shift. At present, the supermarket uses two figures to help with this prediction. These are:
• the number of customers who are predicted to be in the store at any time
• the number of item sales per hour going through the tills.
The owners have asked that you produce a model to help them plan the number of till-trained staff that
will be needed for each shift. In order to keep costs to a minimum, your model should be able to identify
how many staff are required to just provide sufficient cover for any shift. They would like the model to
use both inputs that are currently used to make the prediction, as well as take account of the promise
included in their new marketing campaign. The model should also take account of relevant legislation
covering the amount of breaks staff are entitled to take during an eight hour shift.

Any number it doesn't provide can be made up, also the two numbers it says it gives you must be made up to.

I can't figure out the queue length or the staff needed ect, I'll provide a spreadsheet on how far i got for a one hour period (the reason its called spreadsheet macro is because i did have a print page button on there and it differed from a different one called spreadsheet.)

http://www.megaupload.com/?d=BUWHH8UY