problem with grading of my result

[Arlington, OKOLIKO]

pls house my report sheet in the grade column grades for cells where subjects are not offered it grades F9 when i use this formular =IF(G6>=75,"A1",IF(G6>=70,"B2",IF(G6>=65,"B3",IF(G6>=60,"C4",IF(G6>=55,"C5",IF(G6>=50,"C6",IF(G6>=45,"D7",IF(G6>=40,"E8","F9")))))))) pls help out

[davsth]

=if(g6="","",vlookup(g6,{0,"f9";40,"e8";45,"d7";50,"c6";55,"c5";60,"c4";65,"b3";70,"b2";75,"a1"},2,true))