$4.7-4$ Discuss specific characteristics that could be monitored through variable control charts, the form of data to collect, and the appropriate control chart in the following situations:

a$.$ Waiting time to check in baggage at an airport counter

b$.$ Product assembly time in a hardware company

c$.$ Time to develop a proposal based on customer solicitation

d$.$ Emission level of carbon monoxide for a certain model of automobile

e$.$ Detection of a change in average response time to customer queries when the degree of change is small

f$.$ Changes in blood pressure of a patient over a period of time

g$.$ Acceptance of products manufactured in batches, where batch means of the characteristic selected are determined, with the ability to detect a set proportion nonconformance with a desired level of probability

h$.$ Mortality rate of cardiac surgery patients adjusting for individual patient risk

i$.$ Time to respond to customer queries received at a call center

j$.$ Downtime of Internet service provider to individual customers