Centering a panel

Does anyone know a formula i could use to center a panel?

i am drawing slant panel sinks and need the front panel to cover the fillers (Which the slant panels don't have option for fillers, so I'm using countertop overhang)on each side of the cabinet, i can make the slant panel wider but, it is offsetting the extra width for the fillers, but only to the right of the cabinet. Which throws off my keku clips, i need it to follow the countertop overhang, which will be the filler width

Here is what i have =Width+Countertop_Overhang_Left+Countertop_Overhang_Right-Trim_Panel. Which works for the correct size but not centered.

Thanks