I am trying to sum the columns in row 7 as long as the columns in row 8 are
not blank

Example:

a b c d e
f g h
7 2007 7 3 4 4 6 5 3
8 2008 67 82 76 131

I've tried this formula =SUM(INDEX(1/COUNTIF(B8:M8,B8:M8&"")*B7:M7,0))

however it is adding column 6 that should not be adding giving me a result
of 24 instead of 18.

Please can you help me on this matter. I need to add all columns in row 7 as
long as the respective column in row 8 is not blank.

Thanks,