Hi! Your answer is x - 5
Please see an explanation for a better and clear understanding to your problem!
Any questions about my answer and explanation can be asked through comments! :)
Step-by-step explanation:
To find an expression that is a factor, we simply factor the expression first. Sound a bit confusing? Well It's not that confusing if you understand it.
So what we need to do is to factor the expression first.

Notice anything? Yes, the whole expression has x-term as a variable. We can simply factor the expression by common factor, pulling the variable with the least degree.
We should get
from common factor. However, we can still factor inside the brackets. Inside the bracket, the expression can be factored by two brackets factor. Our x-term which is outside of bracket is a bit useless so you can ignore it. What we want is to factor the expression inside the bracket.

To factor this kind of expression, we use two brackets factoring for a = 1.

To find the first term, we simply multiply x and x to each others.
To find the second term, we add -bx and -ax to each others.
To find the first term, we multiply -a and -b to each others.
So if we follow these steps, our (x-a)(x-b) should be x²-ax-bx+ab = x²-(a+b)x+ab

We only need to find a and b value. Which two numbers multiplying each others and get -15? There are only -5 and 3 or 3 and -5.
That means -5 and 3 | 3 and -5 are our only options.
But what two numbers adding up each others and get -2? That means it's -5 and 3 because -5+3 = -2.
Therefore, from x²-2x-15. Our factors are (x-5)(x+3)
So when the expression is completely factored, the new factored expression is x(x-5)(x+3) Then we look at the choices to see if there are these factors in the choices. From the choices and the expression, the only correct answer is (x-5) because x+5 is not a factor (it doesn't appear), same with other two choices. They seem to be factored but not fully factored.
Hence, the answer is x - 5