Help me to do this assignment on flexible firm model...

How are you to critically evaluate it? What were the exact instructions that you were give concerning this, please?

The first thing that I would suggest trying is the following search.

Flexible Firm Model - Google Search (http://www.google.com/search?hl=en&safe=off&q=Flexible+Firm+Model)

Also, are you asking about Atkinson's Flexible Firm Model? If so, do you have a textbook on the subject?