Ken plays a game with the following constraints:
• He can score 3 or 6 points each turn in the game.
• He can take up to 10 turns in the game.
• He wins the game if he scores 39 points or more.
Winning the game is represented by the given system of inequalities.
6x + 3y ≥ 39
x + y ≤ 10
Ken wins the game.
What is the least number of turns during which Ken must have scored 6 points?