Answer:
The answer is: after 8 games
Explanation:
You can solve this problem in two ways:
                                         Deanna                        Lise
Start with                            $15                            $13
After 1 game                      $14.25                       $12.50
After 2 games                   $13.50                       $12.00
After 3 games                   $12.75                        $11.50
After 4 games                   $12.00                        $11.00
After 5 games                   $11.25                         $10.50
After 6 games                   $10.50                        $10.00
After 7 games                    $9.75                         $9.50
After 8 games                   $9.00                        $9.00
Or you can solve this equation:
= (price of arcade D - price of arcade L) / (Deanna's money - Lise's money)
= ($0.75 - $0.50) / ($15 - $13) = $0.25 / $2 = 8