I think I followed the directives of the "help" instructions but it's not
working and I'm not seeing it.

The Formula is as follows:

=IF(K2<=4.5,"TF",IF(4.5K2<=8,"LF",IF(8K2<=15,"NF ","AF")))

The result is always "AF" if the value in K2 is 4.5 and I think this is the
exact layout the help center gives.

A review from talented eyes would be appreciated.