That said, here's a couple alternate methods to try.
You don't need the AND functions there, as long as you put the if's in the right order.
=IF(A27>=7,"not specified",If(A27>=4,A27*6,IF(A27>=1,A27*5)))
or a little simpler
=IF(A27>=7,"not specified",A27*If(A27>=4,6,IF(A27>=1,5)))