Split base cabinet in 3 unequal vertical section

[crpd12]

I need to build a 57" wide base cab that has 3 vertical sections. I cannot figure a way to do that. The default in the edit box split the cabinet in 2 equal vertical sections  with no way that I can see to specify distances. What am I missing? Is there a way to do that?

Thanks

[TeaTime]

Split it into two equal sizes.

Select one of the new vertical layouts and split it into two equal parts (giving a 25/25/50 layout)

Select the horizontal layout that all these are contained in (likely #2) and hit Equalize.

[Renerabbitt]

"Layout" Indicates a parent section that allows you to specify assignments for the child designations.