Let A, B, and C be the set of people who like product A, product B, and product C respectively.

Accordingly,

n(A) = 21, n(B) = 26, n(C) = 29, n(A ∩ B) = 14, n(C ∩ A) = 12, n(B ∩ C) = 14, n(A ∩ B ∩ C) = 8

The Venn diagram for the given problem can be drawn as

It can be seen that number of people who like product C only is {29 – (4 + 8 + 6)} = 11

It can be seen that number of people who like product C only is

{29 – (4 + 8 + 6)} = 11