You might look for some obvious factor first. In this case, since it ends with 5, it is divisible by 5. Divide 165 / 5 to get the other factor. Then see whether this other factor can be divided into smaller factors. Try small factors (2, 3, 5, 7) first.
prime factorization of 165 = 3 x 5 x 11
factorization of 165 is =3*5*11
165 = 3 * 5 * 11
It's a prime factor.
165 = 3 * 5 * 11
165 = 3*5*11
3 x 5 x 11 = 165
165 = 3 x 5 x 11
3 x 5 x 11 = 165
165 55,3 11,5,3
165 = 3 x 5 x 11
3 * 5 * 11 = 165 Divide by prime numbers until you get a final prime number