I am currently working on setting up a call cost register for my workplace.

Currently, the first cell in columns D, E and I have a formula in them used
to calculate total time of the call, the number of 6 minute units the call
used and the total cost of the call.

However, is the register is expected to be an ongoing thing, I need those 3
formulae to function in ever cell of their respective columns.

Is there any way that this is possible, and if so, could someone please
explain how to set it up.