Below is a possible solution to the challenge Challenge 26 – Find Sum given multiple OR conditions across columns.

Put following formula for the result -

=SUMPRODUCT((COUNTIF($F$1:$I$1,$A$2:$A$20)+
COUNTIF($F$2:$I$2,$B$2:$B$20)>0)*($C$2:$C$20))

The workbook illustrating the solution can be downloaded from Solution - Challenge 26 – Find Sum given multiple OR conditions across columns.