Question 247194
3(x^2-2x-15)
We can factor this expression even further.  
It would look like this: 3(x-5)(x+3), thus the given result was incomplete.


(3x-5)(5x-15)
We can factor (5x-15) even further into 5(x-3), thus this expression was also incomplete.


3(x-5)(x-3)
We can not factor this expression further, thus it is the correct answer to our problem.


(3x-15)(x-3)
We can factor 3 out of the first term, so it would look like this: 3(x-5)(x-3).
Therefore, this expression was also incomplete.


Here some more tips and examples on factoring.
http://www.mathsisfun.com/algebra/factoring.html