1. The problem is to understand the function notation $f(x)$ and what it represents. 2. The notation $f(x)$ means a function named $f$ with input variable $x$. It represents a rule that assigns each input $x$ to exactly one output value. 3. For example, if $f(x) = 2x + 3$, then for any value of $x$, you can find $f(x)$ by substituting $x$ into the expression. 4. Let's say $x = 4$, then: $$f(4) = 2 \times 4 + 3 = 8 + 3 = 11$$ 5. This means when the input is 4, the output of the function $f$ is 11. 6. Functions can be linear, quadratic, or more complex, but the key idea is that each input has one output. 7. To summarize, $f(x)$ is a way to denote a function and its input, and you evaluate it by substituting the input value into the function's formula.