With zeros of 3, -5 and 4, we know that the factors of this polynomial are (x-3)(x+5) and (x-4).
(x-3)(x+5)(x-4) = (x2 +2x - 15)(x-4) = (x3 + 2x2 - 15x - 4x2 - 8x + 60)
Combine like terms
x3 - 2x2 - 23x + 60
The above polynomial satisfies the conditions. It has an x3 term which means it's a 3rd degree polynomial and the coefficient of x3 is 1.
Hope this helps.