Any Tutorial for Promotion Buy X and Y$?

Hi All,
I search all the discussion topic how to create buy X and Y$ but all is buy x free y, I try method Ricky tutorial setup similar but not work, my promo is very simple, buy 4 and get $3 off for selected promotion in tag call B4in3off, I try to setup in same Promo tag but affected my other promotion.

any one have guide to setup this? x = 4 and y = $3 or (selling price x 4)-$3 ?

Thanks

dont think that will work like that, its x for y value, cant imagine a way to calculate a selling price via expression that would work for a math calculation.
hard to offer sugestions without knowing the products/price combinations
what your describing is nor of a calculation/discount flow, sure remember a senario what might work for you where you would use a fixed value calculation with automation to update a ticket discount based on an expression that counts number of applicable products

start here;

use something like product/item tags to set applicable products.