If you have a polynomial

You can find the solution in the divisors of .

If you have found a solution satisfying then you can write your polynomial expresion like this:

Where Q(x) is calculated by dividing P(x) at

In your example your because 3 is satisfying the condition your

P(x)=(x-3)*Q(x)

You will find by dividing at

Hope it's clear

Have a nice day!