Choice Dhoice C is the correct answer. We model this with $0.50x + 30 = 55$, where $x$ is miles.

1. Set up equation: $0.50x + 30 = 55$
2. Subtract 30 from both sides: $0.50x = 55 - 30$
3. Simplify: $0.50x = 25$
4. Divide both sides by 0.50: $x = \frac{25}{0.50}$
5. Simplify: $x = 50$
6. Verify: $0.50(50) + 30 = 25 + 30 = 55$ ✓

So, you drove 50 miles.

Choice Dhoice C is incorrect because this results from adding 30 to 55: $85$, then dividing by 0.50: $170$. You subtract the daily rate.

Choice Dhoice D is incorrect because this is the cost of the mileage ($25), not the number of miles.

Choice Dhoice B is incorrect because this results from multiplying 25 by 0.50: $12.5$. You need to divide.