Which of the following is not a quadratic equation?

• 3x(x + 5) 11 = 2x(x - 2) + 6
• 4x(x + 3) + 7 = 4x(x - 11) + 9
• x(x + 2) 15 = x(2x - 5) + 11
• 4x - 6x + 9 = 0