The first one is clearly linear (why (O(n2))). Same for the last one. Also seco

#1

The first one is clearly linear (why (O(n2))).
Same for the last one.
Also second one is no clear to me to ne O(n2)

#2

O() tells the upper bound. O(n) = O(n^2) but O(n^2) is not necessarily equals to O(n)