Post Office Model: a. Increase in Delay Time (5 to 10 days): vbnet - **Mailing Rate and Delivery Rate Graph:** - Initially, the mailing rate and delivery rate are in equilibrium, both at a constant level. - On day 5, the delay time increases suddenly from 5 to 10 days. - Mailing rate remains constant, but the delivery rate drops temporarily due to the increased delay time. - Over time, the system adjusts, and the delivery rate approaches the new equilibrium. - **Stock of Letters in Transit Graph:** - Initially, the stock of letters in transit is stable. - On day 5, it starts to increase due to the reduced delivery rate. - The stock continues to rise until it reaches a new equilibrium with the increased delay time. b. Decrease in Delay Time (5 to 2.5 days): vbnet - **Mailing Rate and Delivery Rate Graph:** - Initially, the mailing rate and delivery rate are in equilibrium. - On day 5, the delay time decreases suddenly from 5 to 2.5 days. - Mailing rate remains constant, but the delivery rate increases temporarily due to the reduced delay time. - Over time, the system adjusts, and the delivery rate approaches the