Sum cells continuously start from the first non-zero number

I am trying to sum 8 cells continously from the first non-zero number.

For example:
i have sales data from wk1 to wk20, the first wk of sales is wk10, i need a formula to sum from wk10 to wk17. wk#s are column headers.

Please help...........

What happens if the first non-zero number is in week 16, for instance, presumably then you only sum the weekly salse for weeks 16 to 20?

I still want to sum 8 weeks, so in this case, I would want it from wk16 to wk23...

Please.... ^^

o.. sorry, i think i misundersand your question. if I only have 20 weeks of data, in this case, yes, calucation should be only from wk16-wk20.

for my case, I am sure that initial sales are within early period and I do have continuous 8 weeks of sales after the initial sales week.

Thanks for your help.......

^^