The price of a taxi ride is $\mathrm{R} \$ 2.50$ fixed (the "flag-down fare") plus $R \$ 0.10$ per 100 meters traveled. I have only $R \$ 10.00$ in my pocket. Therefore, I have enough money for a ride of, at most, how many kilometers?
(a) 2.5
(b) 5.0
(c) 7.5
(d) 10.0
(e) 12.5
The correct option is (c).

Since the flag-down fare is fixed, we have $10.00 - 2.50 = 7.50$ reais to be spent solely on the distance traveled. Each 100-meter segment costs $0.10, so with $7.50, I can travel $(7.50) / (0.10) = 750 / 10 = 75$ segments of 100 meters each, or $75 \times 100 = 7500$ meters. Since 1 kilometer is 1000 meters, it follows that, with $10.00, I can pay for a ride of up to 7500 meters, or 7.5 kilometers.