(<em>A</em> ∩ <em>B</em>)' is the complement of <em>A</em> ∩ <em>B</em>, or the set of all elements in the universal set <em>U</em> that do not belong to <em>A</em> ∩ <em>B</em>.
<em>A</em> ∩ <em>B</em> is the intersection of <em>A</em> and <em>B</em>, or the set of all elements common to both <em>A</em> and <em>B</em>.
We have
<em>A</em> = {q, s, u, w, y}
<em>B</em> = {q, s, y, z}
so that
<em>A</em> ∩ <em>B</em> = {q, s, y}
Then
(<em>A</em> ∩ <em>B</em>)' = {r, t, u, v, w, x, z}
which makes (c) the answer.
