The roots are x = - 5, x = - 2, x = 4
So the polynomial can become,
(x + 5)(x + 2)(x - 4) = 0
if you want to multiply this out you can get,
(x + 5)(x² - 4x + 2x - 8) = 0
(x + 5)(x² - 2x - 8) = 0
x³ - 2x² - 8x + 5x² - 10x - 40 = 0
x³ + 3x² - 18x - 40 = 0