The graph of the function f(x) = (x − 3)(x + 1) is shown.

which describes all of the values for which the graph is positive and decreasing?

a. all real values of x where x < −1
b. all real values of x where x < 1
c. all real values of x where 1 < x < 3
d. all real values of x where x > 3

Option A. All the real values of x where x < -1

Procedure
Solve the inequality:
(x -3)(x+1)>0
That happens in two cases.

1) When both factors >0
x-3>0 and x+1>0
x>3 and x >-1

The intersection is x >3

2) When both factors <0
x-3<0 and x+1<0
x<3 and x<-1

the intersection is x<-1.

We have obtained that the function is positive for the intervals  x < -1 and x > 3. But in one of those intervals the function is decresing and in the other is increasing.

You can recognize that the function given is a parabola and, because the coefficient of the quadratic term is positive, the parabola opens upward. Then the function is decreasing in the  first interval and increasing in the second interval.

A. is the answer in this question