Merge branch 'development'
Merge branch 'development'
Merge branch 'development'
Merge branch 'development'
Merge pull request #68 from clark-archer/s5.2#8

correct answer for 5.2#8
Merge branch 'development'
Merge branch 'development'
Merge branch 'development'
corrected sign error in answer for 6.2 #15