Respuesta :

Answer:

8

Step-by-step explanation:

The union of the 2 sets are the elements in set A and B

A = { 1, 2, 3, 4, 5, 7 } and B = {3, 4, 8, 9 }

A ∪ B = { 1, 2, 3, 4, 5, 7, 8, 9 }

Note 3 and 4 are not repeated

number of elements in A ∪ B  = 8