I have an list of items with multiple columns of values attached.

Col A = items number (all unique)
Col B = class number (the basis for summarizing)
Col C thru Z = daily values for each item
Row 1 = date

I want to be able to summarize by class number (which I would normally use
SUMIF) and for selected colums (i.e. one or more days)

In other words - what is the sum of class X on day Y

what formula or formulas would I use?