Find the correct answer of the following problem

Problem- A processing line is being designed. There will be five stages with deterministic processing times of (5.0, 4.0, 3.5, 6.0, 4.5). Stages are expected to be 100 percent available, that is, no breakdowns. No precedence relations exist to constrain the order in which stages are sequenced.

Part 1- Show that the production rate is unaffected by the ordering of process stages

Part 2- Show that the time spent on the line by a part is minimized by placing the slowest station first.

Part 3- Is there any advantage to adding buffers? why or why not?

I need expert's assistance to explain the production rate is unaffected by the ordering of process stages.