Although the visual seems rather vague, it actually gives us all of the information that we need to solve the problem. By looking at the graph, we know that both of the x-intercepts are going to be negative. To solve for the x-intercepts of a function, you must set y (or f(x) in this case) to 0 in the equation. When you do this you will get something that looks like 0 = (x+a)(x-b). Now this equation will be equal to 0 if either (x+a) or (x-b) are equal to 0, and since we know that both x-intercepts in the problem must be negative, for the equation to be equal to 0, something must be being added to x on both sides of the equation because that is the only way that a negative number can become 0. And since option D is in the form in which both 3 and 5 are being added to 0, if we set f(x) equal to 0, the x values would be -3 and -5, so D is the correct answer.