Before revision:  The proposed problem is a generalization of the results obtained by Stirzaker and Kupferman where the authors do not present a situation where the sale of a quantity from some goods is constrained by the marketing of another.
After revision:  The proposed problem is a generalization of the results obtained by Stirzaker (Probability and Random Variables: A Beginner's Guide, 1999) and Kupferman (Lecture Notes in Probability, 2009) where the authors do not present a situation where the sale of a quantity from some goods is constrained by the marketing of another.