$4\mathrm{.}2$ Wonder Shed Inc. $($Example $4\mathrm{.}3)$ produces, in addition to the standard model, a deluxe version for the discriminating customer. The production process for the two models is identical and is depicted in Figure $4\mathrm{.}1.$ The activity times for deluxe models is listed in Table $4\mathrm{.}8.$ All the times mentioned represent flow time at the various activities, and include the effects of waiting.

a$.$ Compute the process flow time for producing a deluxe shed.

b$.$ What is the impact on flow time of the process if the flow time of Activity $2$ is increased to $40$ minutes?

c$.$ What is the impact on flow time of the process if the flow time of Activity $3$ is reduced to $40$ minutes?