The problem gives the function $f(x) = 3x - 12$. Part I asks us to determine the value of $f(5)$. Part II asks us to solve the equation $f(x) = 3$.

1. Problem Description

The problem gives the function $f(x) = 3x - 12$. Part I asks us to determine the value of $f(5)$. Part II asks us to solve the equation $f(x) = 3$.

2. Solution Steps

I. To find $f(5)$, we substitute $x=5$ into the expression for $f(x)$:

$f(5) = 3(5) - 12$

$f(5) = 15 - 12$

$f(5) = 3$

II. To solve $f(x) = 3$, we set the expression for $f(x)$ equal to 3 and solve for $x$:

$3x - 12 = 3$

Add 12 to both sides of the equation:

$3x = 3 + 12$

$3x = 15$

Divide both sides by 3:

$x = \frac{15}{3}$

$x = 5$

3. Final Answer

I. $f(5) = 3$

II. $x = 5$