Question $5$

Consider the case study that follows:

When a contractor buys materials at Quality Building Supply, he takes it to the contractor checkout desk. The clerk enters the contractor's name into a point$-$of$-$sale system $($the system$).$ The system displays the contractor record, including his current credit standing. The clerk then opens up a new sales record for the contractor. Next, the clerk scans in the number of the item to be purchased into the system. The system finds the price and product name, then displays these on the screen and adds the item to the sales record. In turn, the clerk enters the quantity of the item. When all items are scanned, the clerk ends the sale. The system calculates the total and checks it against the contractor's credit limit$.$ If the limit is not reached, the system updates the contractor's account by subtracting the amount of the sale from the credit available. If the credit limit is reached, the clerk is alerted to ask for a cash payment. If the contractor does not wish to pay in cash, the clerk cancels the sale. Successfully closed sales are finalized so that the system prints a receipt.

$5\mathrm{.}1$ To describe the above scenario, provide a fully developed use case description.