modifying to 4.2
Merge branch 'day4' into day5
modifying to 4.2 and merge from day4
modifying to 4.2 and merge from day5
modifying to 4.2 and merge from day6
modifying to 4.2 and merge from day7
Merge branch 'day8' into day9
modifying to 4.2 and merge from day8