I dont know the answer but you may find this helpful:
-1 Quart = 1.13 British litres
-Fluid ounce = 0.028 Brtish litres
-1 gallon = 4.546 British litres
-1 Cup is 0.237 British litres
Now all the mesurments are the same i hope this helps a bit.
First year: the depreciation is (35/100) x 20000 = £7000; now the value of the car is £20000 - £7000 = £13000;
Second year: the depreciation is (35/100) x 13000 = £4550; the current value of the car is £13000 - £4550 = £8450.