Identify given sets and their counts

We have set A = {1, 2, 3, 4} with $n(A) = 4$ and set B = {3, 4, 5, 6} with $n(B) = 4$.

$n(A) = 4, \quad n(B) = 4$

Identify the intersection

Identify common elements present in both set A and set B to find $A \cap B$.

$A \cap B = \{3, 4\} \implies n(A \cap B) = 2$

Apply Inclusion-Exclusion Principle

Use the formula for the number of elements in the union of two sets: $n(A \cup B) = n(A) + n(B) - n(A \cap B)$.

$n(A \cup B) = 4 + 4 - 2 = 6$