f(x) is read is function f of x.
Where x is the input variable and function f(x) gives output value of function for x input value.
For the given function, we have f(3).
If we compare f(3) by f(x), the x represented by input value 3.
Therefore, x value is 3 there.
And we also have f(x) =-5.
Because function value is -5. So we can read it as, "for x input value of the the function gives output value -5."
For the asked value of x is just x=3.
