Answer
The puzzle expert must sell 720 copies to break even.
Work Step by Step
Let x = the number of books sold and let y = the number of dollars of expense or income.
Expense: $y = 0.8x + 864 $
Income: $y = 2x $
Use substitution since both equations have been solved for $y$.
$0.8x + 864=2x$
$1.2x=864$
$x=720$
The puzzle expert must sell 720 copies to break even.
