Derive the condition under which adding the Vegan burger increases total profit, given: Regular unit margin $3, Vegan unit margin $2, fixed vegan costs F (training + supplier retainer), and cannibalization rate c (fraction of Vegan sales that would have been Regular). Express the break-even Vegan unit sales as a function of F and c, interpret edge cases (c = 0 and c = 1), and describe how you would estimate c in practice.