Can IF, AND, and OR forumulas be combined?

I would like to be able to do the following in an Excel spreadsheet in a single cell:

=IF(AND(D7="U",D13-D6>=3.1),"NM","X")
or
=IF(AND(D7="P",D13-D6>=15.1),"NM","X")
or
=IF(AND(D7="R",D13-D6>=30.1),"NM","X")
or
=IF(AND(D7="CU<24",D13-D6>=3.1),"NM","X")
or
=IF(AND(D7="CU>24",D13-D6>=1.1),"NM","X")

Is it possible to combine these conditions for a single cell? Also, I only want the "X" to populate if D7="specific letter" AND D13-D6=3.1 is not true. If D7 does not equal the specific letter, then I don't want the "X" to populate.

Cross-Post to: http://www.mrexcel.com/forum/showthread.php?t=350799

Thanks