Using variables in formulas

I have a couple variables that I need to use in multiple calculations for a table. Say one of them is in cell d8. I will need to change it from time to time. I can set up the initial formula, but when I try to paste to next line the cell number changes to d9, etc. Is there any way to be able to copy this specific cell to multiple line items without having to edit each one?

This table has 120 lines, five calculations, and three variables. so editing it item by item is tedious and would take me hours.