What is the most efficient way to separately compute the sum of cells
from rows 1:10, across [an array] of multiple columns, if I want to
assign a numerical value of 100 to all cells that have the value "x" in
the cell?

* I am not allowed to alter the formatting of the worksheet, ergo the
"x" values must remain in the cells;

* I do not want to create extra (ghost) columns just to change the "x"
values to 100.


Essentially, I want to perform this function:

=SUM(A1:A10) (and SUM(B1:B10), etc)

while imposing the condition that =IF((A$1:A$10)="x",100,A$1:A$10)



Thanks in advance for suggestions!