it can take 1200 liters....and it already has 450 liters.....so it needs (1200 - 450) = 750 liters to fill it up to full capacity.
and the price is 81.5 pounds per liter......for 750 liters...
81.5 * 750 = $ 61125 pounds
and he gets a 7.5% discount...
so his discount would be : 0.075 * 61125 = 4584.375 rounds to
$ 4584.38 pounds <== ur answer