Running Total Spreadsheet

Hello,

I need to create a spreadsheet where I can have a running total within a cell that I can add to weekly. For example, we have several jobsite's running at once, and for each jobsite I need a running total for labor hours within one cell, OT hours within another cell, and material cost within another cell. So I need to be able to easily add to the number as I get new totals weekly.

Thank you!