Answer
${{\$}} 30$ million, which we estimate to be much higher than it should be.
Work Step by Step
Using the same graph we obtained in (a), graph the line $x=9$ and find the intersection.
We obtain
$F(9)={{\$}} 30$ million.
Observing the t=4 to t=5 transition (last quarter of 2009 to first quarter of 2010),
we see a substantial drop in sales, which is understandable because of the end-of-year shopping for presents etc.
The last quarter of 2010 is represented by t=8, so we would expect a drop similar to the one last year when t=9.
${{\$}} 30$ million does not fit the pattern, and is, therefore, not a good approximation.
(Perhaps a regression model other than quadratic would be suitable.)
