The correct answer is x^3 - 5x^2 + 16x - 80.
In order to find this, we work backwards. Start by creating true statements for each of the roots.
x = 5
x = +/-4i
Now we can solve all of these until they are statements that equal 0.
x = 5 ----> Subtract 5 from both sides
x - 5 = 0
x = +/-4i ------> Square both sides
x^2 = -16 ---> Add 16 to both sides.
x^2 + 16 = 0
Now we can use the two statements that we have and multiply them to get the polynomial.
(x - 5)(x^2 + 16)
x^3 - 5x^2 + 16x - 80
