product mix optimization problem

Hello everybody
my name is Luca and i'm an italian economics student, and i found some problems while i was solving this exercise that you can download at this link:
www.mediafire.com/?j7g7fewyf4v9zej
or exam july16th.xls

I also included the answers and the plot of the exercise.

Most important: explain which constraints do you use and how you reach the optimal, requested company(469, 30, 331, 32)

Thanks in advance
Luca

PS: If you want to send me the file, my e-mail address is lucabi89@hotmail.it