n= 3; -4 and 3 + 5i are zeros; f(-1) = 123

Answer 1

if 3+5i is a zero, then 3-5i is another zero

x = 3+5i

x-3 = 5i

x^2 -6x +9 = -25

x^2 -6x +34 is a factor

another factor is x+4

multiply the factors together

(x+4)(x^2-6x+34)

= x^3 -2x^2 +10x +136

f(x) =a(x^3-2x^2 +10x +136)

f(-1) = 123 = a(-1 +2 -10 +136) = 127a

a = 123/127

the 3rd degree polynomial with the given zeros is

f(x) = (123/127)(x^3 -23x^2 +10x +136)