Okay, so the prescriptive process model describes traditional software processes.
This is very early in the TB.
This is a bit of an insight question-you have to describe why the use of the tradional models bring structure to SD.
I would think something in the line of:
1) They provide a sequence for the generic framework activities.
2) This forms a structure the designer can follow.
3) They prescribe a set of framework activities that can be used for each project, which will formalize the project.
For b, I would think of disadvantages:
1) Real projects rarely follow sequential flow
2) A working product is only delivered late in project
3) Continuous change...
4) Tight time lines...
I used the opposite of the positives for Agile process to help me here, as they are the reason to prefer it above traditional process
For (a), I would keep to the idea of the prescriptive patterns providing order by prescribing a framework of activities to be followed, etc (also maybe mention the generic framework activities). Then include a mention that they are not so successful, as they fail to accommodate projects in today's changing computer environments (or something along those lines).
For (b), I'm combining the general weaknesses of the evolutionary models with those of the waterfall model, and then finding an "overlap" and mentioning those (4 marks means either 2 or 4 weaknesses needing to be mentioned).