You are tasked with selecting the most suitable packet scheduling policy from the following options:

a$)$ First$-$Come, First$-$Served $($FCFS$)$

b$)$ Priority Scheduling

c$)$ Round Robin $($RR$)$

d$)$ Weighted Fair Queueing $($WFQ$)$

Based on the scenarios described below, choose the best packet scheduling policy for each case by filling in the blank with the appropriate letter $($e$.$g$.,\text{'}$a$\text{'})$:

$1.$ You are designing a ticket$-$selling system where all tickets are priced equally and belong to the same class.

$2.$ Clients have minimum guaranteed service time$/$bandwidth requirements.

$3.$ There are two clients paying the regular price and two clients paying a premium price.

$4.$ There are two clients paying the regular price and one client paying a premium price.