Answer
$n(A \cup B') = 5$
Work Step by Step
$n(A\cup B)$ represents the cardinality (or number of elements) of the set $A \cup B'$.
RECALL:
(1) $B'$ represents the complement of set $B$. The complement of a set is the set that contains all the elements of the universal set $U$ that are not in the set..
(2) $\cup$ represents union of sets. The union of two sets is a set that contains the combined elements of the two sets.
Thus.
$B' = \left\{a, b, g\right\}$
Therefore,
$A \cup B'
\\ =\left\{a, b, c, d\right\} \cup \left\{a, b, c, g\right\}
\\=\left\{a, b, c, d, g\right\}$
$A \cup B'$ has 5 elements. Thus,
$n(A \cup B') = 5$
