Recall that zeroes can be transformed into factors by subtracting them from x. This gives us the following factors:
(x - 1)(x + 3)(x - 4)
Now, if you multiply the first two factors together, you get the following:
(x² + 2x - 3)
Multiply that by the last factor, (x - 4), and you get this:
(x³ + 2x² - 3x - 4x² - 8x + 12)
This can be simplified:
(x³ - 2x² - 11x + 12)
And there's your final answer. Hope this helped!