#### Answer

According to the formula, the percent of American adults who used smart phones to go online in $2013$ is 62%.

#### Work Step by Step

The calculated value underestimates the actual value by 1%.
Consider $S=32+8.7x-0.3{{x}^{2}}$.
Number of years from $2009$ to $2013$ = $4$years.
So, put $x=4$in the given formula.
$\Rightarrow S=32+8.7(4)-0.3{{(4)}^{2}}$
$\Rightarrow S=32+8.7\times 4-0.3\times 16$
$\Rightarrow S=32+34.8-4.8$
$\Rightarrow S=62\,%$
The actual percent shown in the bar graph is 63%, which is greater than the calculated value.
Find the difference of both values.
$=63percent-62percent\,\,=\,\,1percent$
So, the calculated value underestimates the actual value by 1%.