Answer
$(S\cap W)\cup(H\cap C)$ is the set of books that are
either scifi books stored in Washington, or horror books stored in California.
n[ $(S\cap W)\cup(H\cap C)$ ] = 22,000
Work Step by Step
$(S\cap W)\cup(H\cap C)$ is the set of books that are
either scifi books stored in Washington, or horror books stored in California.
n$(S\cap W)$ = 10,000 \quad (intersection of column S and row W)
n$(H\cap C)$ = 12,000 \quad (intersection of column H and row C)
the sets are disjoint (intersection is empty), so
n[ $(S\cap W)\cup(H\cap C)$ ] = 10,000 + 12,000 =22,000
