f(x) means the value of y
The graph has a part down the x-axis which means f(x) < 0
The graph has another part over the x-axis which means f(x) > 0
The value of x for the negative part is from - infinity to 3
Then f(x) < 0 at the interval (-00, 3)
The value of x for the positive part is from 3 to infinity
then f(x) > 0 at the interval (3, 00)
Then the answer is C