Answer
$\text{ approximately $33752$ restaurants}$
Work Step by Step
Since $2013$ is $8$ years after $2005,$ then $x=8.$ Substituting $x=8$ from the equation derived in item $82$a, which is $
y=338.2x+31046
,$ then
\begin{array}{l}\require{cancel}
y=338.2(8)+31046
\\
y=2705.6+31046
\\
y=33751.6
\\
y\approx33752
.\end{array}
Hence, the number of McDonald's restaurants worldwide in $2013$ is $
\text{ approximately $33752$ restaurants}
.$