1. **Stating the problem:** Marwan's car needs 5 liters of gasoline to cover 50 km. We need to find how much gasoline is required for a 200 km trip. 2. **Find gasoline consumption rate per km:** Gasoline per km = $\frac{5 \text{ liters}}{50 \text{ km}} = 0.1 \text{ liters/km}$ 3. **Calculate gasoline needed for 200 km:** Gasoline needed = $0.1 \text{ liters/km} \times 200 \text{ km} = 20 \text{ liters}$ 4. **Answer:** The car needs $20$ liters of gasoline to travel 200 km.