I am trying to get a formula that will do the following:

a score of:
0-9 = normal
10-13 = mild
14-20 = moderate
21-27 = severe
28+ = extremely severe

i tried doing an if function but it won't allow more than 5 (i think) if
functions. could someone please advise if 'if' is the function to use or
whether I should be trying something else?

thanks heaps