Add Condition to Formula

[Karen Smith]

I have to add to the following formula:

=IF(OR(C12={"None";""}),"",VLOOKUP(A12&"-"&F12&"-"&G12,INDIRECT(CHOOSE(MATCH(C12,{"Internal";"External"},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?

 

[Karen Smith]

Please use this one instead.

 

[Herbert Seidenberg]

Create another column, say at A12, that translates B12 into
the text of the worksheet name:
=IF(B12="SM","WC",IF(B12="CD","PLC",""))
WC=WritingCharges
PLC=ProofLayoutCharges
In your formula, replace
"'WritingCharges'!xx:yy"
with
A12&"!xx:yy"