You have to searh the x values that make f(x) = 0
Factoring this equation is very difficult.
You can divide by x+3 and you will find that the equation can be factored as
(x+3)(x-4)^2
That means that x = -3 and x = 4 make f(x) = 0
Then the points are (-3,0) and (4,0).