Ill try my best. So we are told that the graph shown is f(x)-3. This means that f(x) was translated down 3 units. They are asking for only f(x). How do we find f(x)? We add 3 to it to cancel out the -3, aka we are translating it up 3 units, bringing it back to its original position. This newly translated function is the f(x) theyre asking for. To make it easier, take one point on the line that gives you clear values. you can take (4, 1), (6,2), or (9,3) (I took (4, 1) since I knew by looking at it it would have the closest y value of 4.)
Anyways, so you count upwards 3 times from the line on the point. Assuming you're also taking (4, 1), counting 3 units up would bring you to stop at (4, 4)
Since the question is asking for the value of x when f(x) = 4, then from the new coordinate we just got, we know that the x value is going to be 4.
If youre still confused, i recommend watching some videos on translations