I would add ...
what data type resides in H (number, text) ...
what do you want to return if it's an error...
what version of Excel are you running...
Assuming for ex. you're pre 2007... H contains numbers... for error return 0...
=IF(ISNUMBER(MATCH(C73,{6,12,24},0)),LOOKUP(9.99999999999999E+307,CHOOSE({1,2},0,VLOOKUP(D73,IF(C73=6,'Package Mix'!$G$39:$H$45,IF(C73=12,'Package Mix'!$G$6:$H$36,'Package Mix'!$G$48:$H$56)),2,0))),"")
(if you wanted blank rather than 0 you could use a Custom Format to set 0 to null)
Ditto other comments re: INT
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