Chapter 2 - Set Theory - 2.4 Set Operations and Venn Diagrams with Three Sets - Exercise Set 2.4 - Page 92: 42

(A∪B∪C)= {1,2,3,4,5,6,7,8,9,10,11,12}

The set (A∪B∪C), represents the all the elements of the set A and the set B which are not present in set A and the elements of set C which are not present in set A and B. From the given Venn diagram we can conclude that the regions I, II, III, IV, V, VI, VII are belongs to the set (A∪B∪C). The element of these regions are 1,2,3,4,5,6,7,8,9,10,11,12. So, (A∪B∪C)= {1,2,3,4,5,6,7,8,9,10,11,12}