1. **State the problem:** Sam paid a taxi fee of 25 and gave an 18% tip. We want to create a proportion to find the tip amount $x$. 2. **Set up the proportion:** The tip percentage is 18%, which means 18 out of 100. The tip amount $x$ is to the fee 25 as 18 is to 100. So the proportion is: $$\frac{18}{100} = \frac{x}{25}$$ 3. **Explain the proportion:** This proportion states that the ratio of the tip percentage to 100 equals the ratio of the tip amount to the fee. 4. **Solve the proportion for $x$:** Cross multiply: $$18 \times 25 = 100 \times x$$ $$450 = 100x$$ 5. **Isolate $x$ by dividing both sides by 100:** $$\cancel{100}x = \frac{450}{\cancel{100}}$$ $$x = 4.5$$ 6. **Interpretation:** The tip amount $x$ is 4.5. 7. **Find total amount paid:** Add the tip to the fee: $$25 + 4.5 = 29.5$$ So the total amount Sam gave the driver is 29.5.