How do you evaluate $f(4)$ if $f(x) = 2x - 1$?

Hint: This problem deals with finding the value of a particular value of the function which is a given function at a particular given point, or given input. Here given a function which is varying in the variable of $x$, and we have to find out the value of the function at a given particular point. Here we are asked to find the value of the function at a given value of $x$. This can be done by the method of substituting the given value of $x$, in the given function

Complete step by step solution:
Given a function $f(x)$ which is a variable in $x$.
The value of the function at the value of $x$ = 4, is given by substituting the value of $x$ in the given function $f(x)$.
Given that the function is defined as $f(x) = 2x - 1$, now considering it as illustrated below.
Consider the given function $f(x) = 2x - 1$ as shown below:
$ \Rightarrow f(x) = 2x - 1$
Now finding the value of $f(4)$ by assigning the variable $x$ as 4, as shown below:
Substituting the value of $x = 4$, as given below:
$ \Rightarrow f\left( 4 \right) = 2\left( 4 \right) - 1$
Simplifying the above expression as shown below:
$ \Rightarrow f\left( 4 \right) = 8 - 1$
$\therefore f\left( 4 \right) = 7$
Hence, The value of $f(4)$ is equal to 7.

Note: Please note that the value of $f(4)$ is found by substituting the value of the variable $x$ as 4, that is it is done by assigning the value of $x$ to a particular number. Similarly we can find any value of $f(a)$ or $f(b)$ given the function $f(x)$ which is varying in $x$, by substituting the values of $x$ as $a$ or $b$ to get the desired result.