You consume 10 litres for every 100 kilometers you drive. So pretty much what you would do for these type of question is;
2716 km divided by 100 km, so you can see how much quantities of 10L petrol you would consume. You would get 27.16, this pretty much says you need 27.16 units of 10 litre petrol to travel from Perth to Adelaide but to be more precise, we can just do 10 * 27.16 to find the total litres of petrol, you would get 271.6 litres required to complete the trip.
The method I used back in junior years (might be inefficient):
100km -> 10 litres
2716 km -> ?
Cross multiplyish? Like you just switch the arrows to be diagonal, idk whats the proper way;
2716 times 10 / 100
271.6 Litres required
Sorry if this is unclear, I tried simplifying to the best of my ability. For those questions thats what you'd normally use.