Answer
311 million phones
Work Step by Step
$x=26$
$f(x)=-.4x^2+21x+35$
$f(26)=-.4(26)^2+21(26)+35$
$f(26)=-.4*676+546+35$
$f(26)=-270.4+581$
$f(26)=310.6$
311 million phones
Intermediate Algebra (6th Edition)
by Martin-Gay, Elayn
Published by
Pearson
ISBN 10:
0321785045
ISBN 13:
978-0-32178-504-6
Chapter 8 - Section 8.6 - Further Graphing of Quadratic Functions - Exercise Set - Page 527: 87c
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