$($b$)$ A snail has been climbing a wall for many days. Within a day, its climb $($in $cm)$ is

equal to: $3$ times the climb of the previous day minus $2$ times the climb of the

previous, previous day $($two days before$)-$ this happen because it was slipping

down the wall everytime it fell asleep at night. Note: Its yield for its first day

climb is $1cm$ and its yield for the second day climb is $2cm.$