<p>There is an easier way to do 5 than trying to guess numbers that work.</p>
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<p>A) (a + b + c + d + e + f)/6 = -6 Given</p>
<p>B) a+b+c+d = 10 Given</p>
<p>(10 + e + f)/6 = -6 Substitute B into A</p>
<p>10 + e + f = -36 Multiply 6 by both sides</p>
<p>e + f = -46 Subtract 10 from both sides</p>
<p>e + f = -46 so (e + f)/2 = -23</p>
<p>So the answer is C) -23</p>