Add number to cell 1, add it to cell 2,

I am making a weekly work progress sheet. I am an electrical contractor and want to be able to input my weekly quantities in say cell f6. I want to add that to cell i6. I want to be able to delete the number in cell f6 every week to input the new quantity for the week and I want cell i6 to keep adding the total.

Lets say we are installing conduit. week 1 we install 300'. I will put that into cell f6 and cell i6 will copy that number 300'. Next week we have 325' of the same conduit I want to delete the 300 from cell f6 and put in 325 but I want cell i6 to say 625. The following week we install 400' of the same conduit. I want to delete the 325 from cell f6 and put in 400' and have cell i6 show 1025'.

Is this possible and how would I do that?

Thanks

Andy