Answer
The number of pages will reach 1000 by the $16th$ edition.
Work Step by Step
Using the model found in part (a), $L=29n+545$
we solve for n when $L=1000.$
$1000=29n+545\qquad/-545$
$455=29n\qquad/\div 29$
$15.7\approx n$
The number of pages will be 1000 by the $16th$ edition.