<p><span style="color:#8e44ad;"><span style="font-size:20px;">Deductions from the Given Information</span></span></p>
<p>We know the following about probabilities:</p>
<p>$P(E)+P(F)-P(E\,AND\,F)+P(Neither) = 1$</p>
<p>We can substitute in the probability for both, which we know to be $0.42$:</p>
<ul>
<li>$P(E)+P(F)- 0.42 + P(Neither) = 1$</li>
<li>$P(E) = 1 + 0.42 - P(Neither) - P(F)$</li>
<li>$P(E) = 1.42 - P(Neither) - P(F)$</li>
</ul>
<p><span style="color:#27ae60;"><span style="font-size:20px;">Solving the Problem</span></span></p>
<p>We can use the E<strong><span style="color:#8e44ad;">qual not Equal Strategy</span></strong> here:</p>
<p>If $P(Neither) + P(F) = 0.84$, then $QA = QB$</p>
<p>If $P(Neither) + P(F) \neq 0.84$, then $QA\neq QB$</p>
<p>So, the answer would be <span style="color:#27ae60;">D</span>.</p>