20.) How do I find the zeros of the function algebraically?

Question

ex1) f(x)= x^3 -4x^2 -9x +36

ex3) f(x)= 3 +(5/x)

ex7) f(x) = (2x^2-9)/ (3-x)

Answer 1

I figured out 1. How do I do ex 3 & 7

Answer 2

I figured out 3 already and got x=-5/3

1.) -3, 3, 4

Answer 3

ok I'm actually stuck on ex.7