24/30 = 12/15 = 4/5
this is the simplified form
13km 500m = 13.5 km
The car consume 1 liter of petrol every 6 km, so for 13.5 km it will consume: 13.5 x 1 / 6 = 2.25 liters
Now, keep in mind that, we'll be using 25mile intervals, notice, that at a cost of 200 bucks, it went for 50 miles, now the charges are just for every 25miles only, so, if you drive 30 miles, you pay for 25miles and if you drive for 49 miles, you still only pay for 25 miles, but because 50/25 is 2 intervals, then if you drive for 50 miles, you're paying for 2 intervals of 25miles, not just one.
now, also let's keep in mind that, when the car was driven for 200 miles, that's 200/25 or 8 25mile intervals, so the 25mile charge kicked in 8 times.