It depends on the cost of said petrol and the efficiency of the vehicle in "miles per unit of petrol". You didn't supply enough information.
From Cardiff to Glasgow is some 400 miles and would cost about £75 in petrol.
At 15 miles per gallon, 7 gallons of petrol.
Depending on driving conditions - about 2.5 gallons.
It would cost (2.4) times (the cost of one gallon petrol). Also, add cost of tolls, food, etc.
500 miles is always 500 miles unless it's nautiical miles. I'm not sure if 500 miles in petrol would be classed as nautical miles.
300 dollars
274
£10 approx dependent on the price of a liter at the time
It depends on how fast you travel.
Depends on the fuel mileage that the vehicle you are driving gets and the price of fuel along the way.
The cost of petrol for 1 mile will depend on the fuel efficiency of your vehicle (miles per gallon) and the current price of petrol. As a rough estimate, if your car gets 25 miles per gallon and petrol costs $3 per gallon, then it would cost you around $0.12 per mile in petrol costs.