Kellogg's sells many breakfast cereals, including Corn Flakes, Rice Krispies, Frosted Flakes, Raisin Bran, and Special K. This is an example of the breadth of the Kellogg's product mix.
Product line depth (not breadth) equals the number of products within a product line, as in this question.

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Quizplus · Accepted Answer

The example given is about the breadth of Kellogg's product mix, which refers to the variety of different product lines (types of cereals) they offer, not the depth within a single product line.

Kellogg's Sells Many Breakfast Cereals, Including Corn Flakes, Rice Krispies