To evaluate $f(x) = 3x$, you need to substitute a specific value of $x$ into the function.

For example, if $x = 2$, then:

$f(2) = 3(2) = 6$

Do you have a particular value of $x$ you'd like to evaluate, or should I choose one for demonstration?

Follow-up Questions:

1. What is the result of $f(x)$ when $x = -1$?
2. How would the function change if it were $f(x) = 3x + 5$?
3. Can you graph the function $f(x) = 3x$?
4. What happens to $f(x)$ as $x \to 0$?
5. What is the inverse of the function $f(x) = 3x$?

Tip: Linear functions like $f(x) = 3x$ always produce a straight line when graphed.