fixed numbering
Fixed error in chapter 5.
Updated pdf.
added solution environment
created files for chapter9-12
chapter is too long to type
added files for chapters 2-4
proposed solutions for chapter 2
proposed solutions to chapter 3
proposed solutions to chapter 4
proposed solutions for chapter 9
added a few chapter 10 solutions
proposed soltuions to chap10
more proposed solutions
updated old tex files and added more solutions to chap11