For a journey of $25 \mathrm{~km}$, she spends 3 liters, so to travel $100 \mathrm{~km}$, Maria will spend $4 \times 3=12$ liters. Therefore, to travel $600 \mathrm{~km}$, the car will consume $6 \times 12=72$ liters. Since each liter costs 0.75 reais, then 72 liters will cost $0.75 \times 72=54$ reais.
2 - Note that we can use the Rule of Three to calculate how many liters are consumed in $600 \mathrm{~km}$ :

| 3 liters |  | $25 \mathrm{~km}$ |
| :--- | :--- | :--- |
| $x$ liters |  |  |
|  |  | $600 \mathrm{~km}$ |

Since this rule of three is direct, we have: $25 x=3 \times 600 \Rightarrow x=3 \times \frac{600}{25}=72$ liters.

Solution 3 - Since $600=25 \times 24$, the car will consume $24 \times 3=72$ liters.