1. The problem asks for an expression representing the distance a fish swims in $x$ hours, given its speed is 12 miles per hour. 2. The formula for distance when speed and time are known is: $$\text{Distance} = \text{Speed} \times \text{Time}$$ 3. Here, speed is 12 miles per hour and time is $x$ hours. 4. Substitute the values into the formula: $$\text{Distance} = 12 \times x = 12x$$ 5. Therefore, the expression representing the distance the fish swims in $x$ hours is $12x$. 6. Among the options, this corresponds to option C. Final answer: C. 12x