Problem #1: Construct Action/Response table from narrative
 

1. Approach clerk's counter with letter in an addressed envelope.	2. Ackmowledge customer.
3. Present letter. Request mail letter via certified mail.	4. Accept letter. Weigh letter and compute postage due. Total certified mail and return receipt costs. Record them onto PS Form 3000. Request total in payment from the customer.
5. Pay clerk the requested amount.	6. Accept money from the customer. Affic postage onto the envelope. Stamp receipt. Attach certified mail part of PS Form 3000 to the envelope. Add article number to PS Form 3811. Give receipt part of PS Form 3000 and PS Form 3811 to the customer. Ask the customer to complete both sides of PS Form 3811.
7. Accept receipt and PS Form 3811. Complete both sides of PS Form 3811. Return PS Form 3811 to the clerk.	8. Accept completed PS Form 3811. Attach PS Form 3811 to the envelope. Place the envelope in certified mail. Ask customer to complete the top part of PS Form 3000.
9. Fill out the top of PS Form 3000. Leave the post office.

Problem #2: Construct UML Use Case Diagram from the Action/Response table

Problem #3: Construct a preliminary list of the objects in this system

Letter: Has information about destination (address), source (return address), and might have any of a number of states (postage due, postage paid, in mail, arrived at destination.)
Form 3811 and Form 3000: Stores the information that the form should contain.  (A more sensible object model may be constructed if we knew what information was on this form.)
Customer:  Stores any identity of the customer's that may be important to the post office, as well as a balance of payment due and received.
Customer Queue: Stores customers that have not yet been served.
Mail Queue and Certified Mail Queue: Stores letters that are ready to be mailed.  This would not be an object in the system of the Letter object had information about whether or not the letter could be mailed.
Other objects:  Other objects are certainly possible; the value and quality of an object decomposition is not really known for sure until the system is actually implemented and maintained.