1. The problem is to express a function in the form $f(x)$. 2. A function $f(x)$ represents a rule that assigns each input $x$ to exactly one output. 3. For example, if the function is defined by the rule "multiply by 2 and add 3," then the function is written as $f(x) = 2x + 3$. 4. To write any function in $f(x)$ format, identify the rule that relates $x$ to the output and write it as $f(x) = \text{rule involving } x$. 5. Without a specific rule or expression given, the general form is simply $f(x) = \text{expression in } x$. 6. If you provide a specific function or rule, I can write it explicitly in $f(x)$ format.