formula to set for adding total by month

[aw]

Could anyone can help if I need to sum "exp1" & "exp2" by refering to column
up to cell to be inputed in separated cell. eg. C1 in this case

cell to input > feb (cell C1)

jan feb mar

xxx
exp 1 100 300 500
exp 2 200 400 600
xxx
xxx

 

[Bob Phillips]

Look at INDIRECT in help.