I have to add to the following formula:

=IF(OR(C12={"None";""}),"",VLOOKUP(A12&"-"&F12&"-"&G12,INDIRECT(CHOOSE(MATCH(C12,{"Internal";"Exter nal"},0),"'Writing
Charges'!D3:E60","'Writing Charges'!G3:H60")),2,0)*I12)

the next part needs to be
If B12="SM" than don't add anything
If C12="NONE" than don't add anything
If C12="Internal";"External" then VLOOKUP(A12&"-"&F12 than "'Proof Layout
Charges'!c3:d31","'Proof Layout Charges'!c3:d31")),2,0)*I12

Can anyone help?