//adds the litres purchased and the cost of a fuelpurchase to a vehicle
public void AddFuelPurchase(FuelPurchase fp)
{
TotalCost += fp.Cost;
TotalFuelPurchased += fp.litres;
}
public void AddFuelPurchase(FuelPurchase fp)
{
TotalCost += fp.FuelCost;
TotalFuelPurchased += fp.PurchasedAmount;
}