The answer to this depends on several factors.
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.
It would cost (2.4) times (the cost of one gallon petrol). Also, add cost of tolls, food, etc.
300 dollars
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.
£10 approx dependent on the price of a liter at the time
Depends on the fuel mileage that the vehicle you are driving gets and the price of fuel along the way.
That is totally dependent on the price for the petrol and and the miles per gallon rating on the vehicle.
18,800 divided by 35 = 537.14 gallons of fuel required to travel this distance. 537.14 x 6 pounds = 3,222.84 pounds.
$300.15
That would depend on the price of fuel, in the UK you would pay around £5.24 per imperial gallon of petrol (September 2010), that would cost around £18.88 to drive 90 miles.
That depends on your fuel mileage.