Duct Pressure Loss Calc

I am attempting to set up a worksheet to calculate the pressure loss through duct work for HVAC. I could not find any examples in the collab and I was hoping someone can point me in the right direction. I have a feeling (still looking into it) that I may have to solve using user-defined functions. I'm still confussed by user-defined functions, so a good place for a primer would also be appreciated.

Thank you for for any assistance