Given that,
The camera sights the stadium at a 7 degree angle of depression.
The altitude of the blimp i slide 300 m.
To find,
The line of sight distance from the camera to the stadium.
Solution,
If we consider a right angled triangle. Let x is its hypotenuse i.e. the line of sight distance from the camera to the stadium. Using trigonometry :

So, the line of sight is at a distance of 2461.65 m from the camera to the stadium.
F(4) value is 6.
I believe it would work like this:
f(x) is being turned into f(4), so 4 would equal x. Put 4 into the equation 3x-6, and you get 12-6, which gives you 6. So the value of f(4) is 6. I hope this helps!